Monthly Archives: December 2019

Friday Fellow: Common Fish Louse

by Piter Kehoma Boll

We all know that crustaceans comprise the most morphologically and ecologically diverse group of arthropods. One peculiar clade is that of the arguloids or fish lice.

As you may infer from the common name, the fish lice are parasites of fish, and eventually other vertebrates. One of the most common an well-known species is Argulus foliaceus, known as the common fish louse.

The common fish louse is found in freshwater bodies of Europe and parasitizes many different fish species. Their only food is fish blood, so they are forced to look for a host as soon as they hatch from their eggs. Once they find a fish, they attach firmly to its skin and remain there for most of their life. They only leave the host to mate or if the host dies and they need to find a new one. Trouts, perches, roaches and sticklebacks are some common hosts of the common fish louse.

Watch some eggs hatching and the larvae that come out of them.

The first and only larval stage, called metanauplius, measures less than 1 mm in length and has long and plumose antennae and palps but relatively short legs. The thoracic legs have claws, though, and help them to attach to the host. In the second stage, already a young adult, the antennae became much shorter but the legs grow more, especially the abdominal legs, which became plumose like the antennae used to be. From there on, the body remains with a more or less constant shape but increases in size, reaching about 6 mm at the 11th stage.

Several common fish lice parasitizing a brown trout in Denmark. Photo by iNaturalist user mikkel65.*

In natural environments, the number of common fish lice per fish is usually small and they do not harm the host that much. However, in confined habitats, such as fish farms, they can reach high densities and end up causing a high fish mortality.

Just like many other external parasites or other types of blood-sucking animals, the common fish louse can serve as an intermediary host for some nematode parasites that infect freshwater fish. The larval stages of the worm reach the fish louse when he feeds on infected fish and remain in its body, eventually infecting a new fish when the crustacean abandons its current home and searches for another one.

Thus, sometimes the main problem that fish face is not the fish louse itself, but rather its hitchhikers.

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More maxillopods:

Friday Fellow: Glacial calanus (on 1 July 2016)

Friday Fellow: Common Goose Barnacle (on 31 May 2019)

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Harrison AJ, Gault NFS, Dick JTA (2006) Seasonal and vertical patterns of egg-laying by the freshwater fish louse Argulus foliaceus (Crustacea: Branchiura). Diseases of Aquatic Organisms 68:167–173.

Molnár K, Székely C (1998) Occurrence of skrjabillanid nematodes in fishes of Hungary and in the intermediate host, Argulus foliaceus. Acta Veterinaria Hungarica 46(4): 451-463.

Pasternak AF, Mikheev VN, Valtonen ET (2000) Life history charactheristics of Argulus foliaceus L. (Crustacea: Branchiura) populations in Central Finland. Annales Zoologici Fennici 37: 25–35.

Rushton-Mellor SK, Boxshall GA (1994) The developmental sequence of Argulus foliaceus (Crustacea: Branchiura). Journal of Natural History 28(4): 763–785. doi: 10.1080/00222939400770391

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Filed under crustaceans, Friday Fellow, Parasites

Friday Fellow: Hippo Fly

by Piter Kehoma Boll

If you ever lived in the countryside or visited the country side often, you may be aware of the existence of an annoying group of flies that bite humans and other animals, the so-called horseflies that make up the family Tabanidae. Today’s fellow is a member of this family and is known scientifically as Tabanus biguttatus and commonly as the hippo fly.

This species is found throughout Africa and some areas of Middle East, being, apparently, much more common in eastern and southeastern Africa. As with all tabanid flies, the hippo fly has an aquatic to semiaquatic larva that lives in muddy areas. They are ferocious predators and prey on other animals living in the same habitat, such as larvae of crane flies, and can also feed on dead animals. When the larvae are about the pupate, they construct a mud cylinder, cover it with a circular lid with only a small hole to allow them to breathe, and remain there until they turn into adults. This is, apparently, a strategy to avoid desiccation.

Male hippo fly in South Africa. Photo by Ryan Tippett.*

Adult hippo flies measure about 2 cm in length, being relatively large tabanids, and show a considerable sexual dimorphism. As all tabanids, males are smaller but have larger compound eyes than females. The eyes of the males are so large that they touch each other, covering the whole top of the head. Females, on the other hand, have smaller eyes with a considerable space between them. The body of both males and females is predominantly black. Males have two white triangular spots on the abdomen while females have the thorax covered with white to golden hair with a small heart-shaped black spot in the middle.

Female hippo fly in South Africa. Photo by iNaturalist user bgwright.*

Male adult hippo flies are harmless and feed only on nectar. Females, on the other hand, need mammal blood to obtain enough protein for egg development. They attack many large mammal species, including humans, cattle and even dogs, but they have a strong preference for hippos, hence the common name.

Two female hippo flies feeding on a southern warthog (Phacocerus africanus spp. sundevallii). Photo by iNaturalist user happyasacupake.*

Hippo flies, like all tabanids, are diurnal flies and love sunny places. They avoid shaded areas, so animals in open areas are much more vulnerable. To get blood, a female approach animals and cut their skin with her sharp mouthparts, making them bleed and licking up the blood. This bite is very painful, which you may know if you have ever been bitten by a horsefly. If undisturbed, the fly can remain up to three minutes drinking blood.

Closeup of the two flies on the warthog’s back. Photo by iNaturalist user happyasacupake.*

The blood-drinking activity of female hippo flies, and of tabanids in general, make them likely mechanical vectors of some parasites, including species of the flagellate genus Tripanossoma, as well as Bacillus anthracis, the bacteria that causes anthrax, which is a considerably common disease in hippos.

Hippo flies are such a nuisance for hippos that their behavior is heavily affected by the flies’ presence, much more than by the presence of any large predator. Most of the time, hippos remain in the water solely to get rid of these annoying insects.

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More Dipterans:

Friday Fellow: Housefly (on 12 October 2012)

Friday Fellow: Cute Bee Fly (on 29 July 2016)

Friday Fellow: Bathroom Moth Midge (on 5 April 2019)

Friday Fellow: Blue Paddled Mosquito (on 27 September 2019)

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Callan EM (1980) Larval feeding habits of Tabanus biguttatus and Amanella emergens in South Africa (Diptera: Tabanidae). Revue de Zoologie Africaine 94(4): 791-794.

Tinley KL (2009) Some observations on certain tabanid flies in North-Eastern Zululand (Diptera: Tabanidae). Proceedings of the Royal Entomological Society of London. Series A, General Entomology, 39(4-6), 73–75. doi: 10.1111/j.1365-3032.1964.tb00789.x

Tremlett JG (2009) Mud cylinders formed by larvae of Tabanus biguttatus Wied. (Diptera: Tabanidae) in Kenya. Proceedings of the Royal Entomological Society of London. Series A, General Entomology, 39(1-3), 23–24. doi: 10.1111/j.1365-3032.1964.tb00779.x

Wiesenhütter E (1975) Research into the relative importance of Tabanidae (Diptera) in mechanical disease transmission. Journal of Natural History, 9(4), 385–392. doi: 10.1080/00222937500770281 

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*Creative Commons License This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

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Filed under Entomology, Friday Fellow

Friday Fellow: Emerald Ash Borer

by Piter Kehoma Boll

It’s time for our next beetle and this time our fellow is a species that spent its first century after discovery without calling much attention but then something happened. Its name is Agrilus planipennis and is commonly known as the emerald ash borer.

An adult emerald ash borer in Virginia, USA. Photo by Bryan Wright.*

Native from East Asia, the emerald ash borer is found in southeastern Russia, Mongolia, northern China, Korea and Japan. Adults measure about 8.5 mm in length and have a metalic green color on the head, pronotum and elythra, and an iridescent-purple metalic color on the dorsal side of the abdomen, seen when the wings are open. They live in the canopy of ash trees (Fraxinus spp.) during spring and summer and feed on their leaves.

After about a week as adults, the emerald ash borers start to mate. Females remain on the trees and males hover around looking for them. Once a female is located, the male drops over her and they start to mate. After mating is concluded, females live for some more weeks and typically lay about 40 to 70 eggs, although some live longer and may lay up to 200 eggs.

Dorsal view of an emerald ash borer with open wings showing the iridescent-purple abdomen.

The eggs are laid between crevices or cracks of the bark and hatch about two weeks later. The newly hatched larvae chew through the bark, reach the inner tissues of the trunk and start to feed on them. They reach up to 32 mm in length in the fourth instar, more than three times the length of the adult, and pupate during spring, emerging as adults soon after. In China, adults emerge from the trees in May.

A larva inside an ash tree in Pennsylvania, USA. Credits to the Pennsylvania Department of Conservation and Natural Resource.**

In its native area, the emerald ash borer can be a nuisance but is not highly problematic to ash trees because it occurs in low densities. However, in 2002, the species was found in the United States feeding on local ash species. Since the emerald ash borer has no natural predators in North America and the ash species in this continent did not evolve to be resistant to infection, it started to spread very quickly. In less than two decades, the beetle has killed millions of ash trees and is a serious threat to the more than eight billion ash trees found in North America. With the death of ash trees, North American forests become vulnerable to more invasive species, which will only worsen the scenario.

Damage caused by the larvae to a tree in New York state, USA. Photo by iNaturalist user bkmertz.*

In order to control the spread of the emerald ash borer, ash trees are treated with pesticides. Four parasitoid wasps from China known to attack only the emerald ash borer have also been released in North America to help control the spread and their success is still being assessed. Traps, such as glue-covered purple panels, which are visually attractive to the beetles, are also used to capture the animals and determine the extent of the invasion.

Once more, a completely fine species has led to an ecological disaster due to human influence and now we are running to find ways to avoid an ecosystem collapse throughout an entire continent.

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Francese JA, Mastro VC, Oliver JB, Lance DR, Youssef N, Lavallee SG (2005) Evaluation of colors for trapping Agrilus planipennis (Coleoptera: Buprestidae). Journal of Entomological Science 40(1): 93-95.

Liu H, Bauer LS, Miller DL, Zhao T, Gao R, Song L, Luan Q, Jin R, Gao C (2007) Seasonal abundance of Agrilus planipennis (Coleoptera: Buprestidae) and its natural enemies Oobius agrili (Hymenoptera: Encyrtidae) and Tetrastichus planipennisi (Hymenoptera: Eulophidae) in China. Biological Control 42(1): 61-71. doi: 10.1016/j.biocontrol.2007.03.011

Wang XY, Yang ZQ, Gould JR, Zhang YN, Liu GJ, Liu ES (2010) The biology and ecology of the emerald ash borer, Agrilus planipennis, in China. Journal of Insect Science 10(1): 128. doi: 10.1673/031.010.12801

Wikipedia. Emerald ash borer. Available at < >. Access on 9 December 2019.

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**Creative Commons License This work is licensed under a Creative Commons Attribution 3.0 Unported License.

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Filed under Conservation, Entomology, Extinction, Friday Fellow

A balanced diet may kill you sooner… if you are a land planarian

by Piter Kehoma Boll

There’s one thing that I should do more often here, and that is presenting my own research for the readers of the blog, so today I am going to do exactly that.

As you may know, the group of organisms with which I work is the family Geoplanidae, commonly known as land planarians. Here in Brazil, the most speciose genus is Obama, of which I have talked in previous posts. This genus became considerably famous after one of its species, Obama nungara, became invasive in Europe, which called attention of the public especially because of the curious name of this genus, even though it has nothing to do with the former president of the United States.

Anyway, during my Master’s study, it became clear that species in the genus Obama feed on soft-bodied invertebrates, mainly slugs and snails, although some species also feed on earthworms or even other land planarians. Obama nungara, for example, feeds on all three groups, although it seems to have some preference for earthworms.

A specimen of Obama anthropophila with its testicle freckles. Photo by myself, Piter K. Boll.*

One common species of Obama in urbans areas of southern Brazil is Obama anthropophila, whose name, meaning “lover of humans” is a reference to this habit precisely. This species has a uniformly dark brown dorsal color, sometimes mottled by the mature testicles appearing as darker spots on the first half of the body. The diet of this species includes snails, slugs, nemerteans and other land planarians, especially of the genus Luteostriata, and more especially of the species Luteostriata abundans, which occurs very often in urbans areas too.

Watch Obama anthropophila capture different prey species.

So I wondered… if O. anthropophila feeds on different types of invertebrates, does it mean that each type provides different nutritients, so that a mixed diet is necessary or more beneficial than one composed of a single prey type? To assess that, I divided adult specimens of O. anthropophila into three groups, each receving a different diet:

Group Dela: fed only with the common marsh slug, Deroceras laeve
Group Luab: fed only with the abundant yellow striped planarian, Luteostriata abundans
Group Mixed: fed with both prey species in an alternating way

The results were not what I expected. The Mixed group showed a lower survival rate than the groups receiving a single diet. Another interesting feature was that the Mixed group showed a tendency to skip the slug meal and eat only the planarian after some days receiving the alternating prey types.

Based on the hypothesis that a mixed diet is more nutritious, I was expecting the Mixed group to have the best performance, or at least being similar to the single-diet groups if there was no increase in nutritional value with an additional prey type. However, the results indicate that a mixed diet may be bad for the planarian, at least if the animal has to eat a different food on every meal.

We don’t know what causes this, but my idea is that maybe different prey types demand different metabolic processes, such as the production of different enzymes and stuff, and having to constantly reset your metabolism is too costly. As a result, the fitness of specimens receiving such a diet decreases and the animals start to avoid one of the food types, because eating less is less dangerous than mixing food.

A “pregnant” Obama anthropophila about to ley an egg capsule. Photo by myself, Piter K. Boll.*

Another interesting aspect is that planarians receiving a mixed diet, even though they died earlier, laid heavier egg capsules than the single-diet groups. Heavier egg capsules generally mean that they have more embryos or are more nutrient for the embryos, increasing the reproductive success. But how can a dying animal be better at reproducing than a healthy one?

Well, this may be related to the terminal investment hypothesis. It is thought, and proven in some groups, that an organism may increase its investment on reproduction when future reproductive events are not expected, i.e., when the organism “realizes” it is about to die, it puts all its effort to reproduce in order to garantee that its genes will pass successfully to future generations.

We cannot be sure about anything yet. More studies are necessary to better understand the relationship of land planarians and their food. What we can assure is that, just like Obama nungara, O. anthropophila may end up in Europe or anywhere else soon because its relatively broad diet and its proximity to humans make it a potential new species to be spread accidentally around the world.

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Boll PK, Marques D, & Leal-Zanchet AM (2020) Mind the food: Survival, growth and fecundity of a Neotropical land planarian (Platyhelminthes, Geoplanidae) under different diets. Zoology 138: 125722.

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Filed under Ecology, Evolution, flatworms, worms

Friday Fellow: Black-Tailed Red Sheetweaver

by Piter Kehoma Boll

There are many spider groups that are well-known by the general public: tarantulas, jumping spiders, wolf spiders, orbweavers… but one of the groups with a very large number of species, the family Linyphiidae, is usually unnoticed.

Spiders of the family Linyphiidae are commonly known as sheetweavers because of the shape of their webs. A common species in the eastern United States, especially in the southeast, is Florinda coccinea, known as the black-tailed red sheetweaver or red grass spider. Being only 3 to 4 mm long, the black-tailed red sheetweaver has a red body with a small black tip on the abdomen. The legs are reddish-brown to black.

Female black-tailed red sheetweaver in Mississipi, USA. Photo by Tiffany Stone.*

Males and females are very similar in size, with males being slightly smaller. They can be easily distinguished by the abdomen and the pedipalps as in most spiders. Females have smaller pedipalps and a rounder abdomen, while males have larger pedipalps with a round expansion at the tip and slenderer abdomens.

A male in Florida, USA. Photo by iNaturalist user rsnyder11.*

The web of the black-tailed red sheetweaver, just like in other sheetweavers, consists of an horizontal sheet over which some additional threads above. Flying insects, when they colide with the threads, fall on the sheet and are captured by the spider.

Typical aspect of the black-tailed red sheetweaver’s web as seen in the field, here covered by dew droplets. Photo by iNaturalist user ndrobinson.**

The mating behavior of the black-tailed red sheetweaver begings with the male entering the female’s web. He usually cuts off part of the female’s web and deposits new web at the same place. After this, he approaches the female, touches all her legs with his two anterior pairs of legs, and then start the pseudopulation, in which he introduces the tubes of his palps into the female genitalia but, as they are still empty, fertilization cannot occur. After some time playing like this, the male builds a small triangular web sheet and deposits a drop of sperm on it. He then collects the sperm with his pedipalps and approaches the female once more, this time breeding her for sure.

Again, the ecology and life-history of the black-tailed red sheetweaver is not very well studied. And the same is true for almost all species in the family Linyphiidae, even though it is the second largest spider family on the planet. They are too tiny for most of us to care.

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Robertson MW, Adler PH (1994) Mating behavior of Florinda coccinea (Hentz) (Araneae: Linyphiidae). Journal of Insect Behavior 7(3): 313–326. doi: 10.1007/BF01989738

Wikipedia. Blacktailed red sheetweaver. Available at < >. Access on October 23, 2019.

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Filed under Arachnids, Friday Fellow, Spiders