#true flies

Horsing Around with Horse Flies

Though horse flies are regarded worldwide as pests, members of the family Tabanidae are an important part of their natural environments. Adults feed on nectar, and some are specialized pollinators that have evolved to only collect from a few select flowers. Just like mosquitoes, only female horse flies feed on blood. Reproduction requires moisture; typically clean, stagnant or slow-moving water. Because of this, some species of horse fly are excellent indicators of an ecosystem’s health. Their role as disease carriers is also a valuable part of any functioning ecosystem; diseases can keep animal populations in check, and sick animals are often easier targets for predators. Horse flies themselves are also a juicy treat for amphibians, reptiles, and birds, as well as insects like wasps and spiders.

There are about 4,455 species of Tabanidae flies, the majority of which reside in the genus Tabanus. Most species share the same general body shape: a large head, a fat body supported by six legs, and one pair of wings. However, there are many variations on this pattern in terms of size, color, and specialized appendages. The smallest horse flies are only 5 mm (0.19 in) long, while the largest is over 30 mm (1.18 in). Like other flies, horse flies have a set of compound eyes made up of thousands of ommatidia: specialised units which allow them to combine input from multiple angles. The resulting image has a poor resolution, but it’s useful for detecting rapid movement-- an important tool when trying to avoid predators. The eyes of male horse flies are holoptic, meaning they meet in the middle to give the appearence of one continuous eye.

Horse flies go through a complete metamorphosis, also known as holometabolism, over the course of their lives. Eggs are laid of clusters of anywhere from 100 to 1000, typically on plants near a source of fresh water. After about six days, the larvae hatch and drop down into the water or burrow into the moist ground, and use a respiratory siphon to pull air from the surface. In temperate regions the grubs enter a stage of dormancy, while tropical horse flies develop year-round. While in this stage individuals consume a number of other insect larvae, worms, and aquatic insects. Once fully developed the horse fly larva pupates for one to three weeks, after which it emerges as a fully-grown adult. Mating can occur as soon as the wings have fully expanded, although female horse flies need to feed on large quantities of blood before depositing the egg mass, in order to provide her young with the nutrients they need to develop.

Conservation status: No horse fly species has been evaluated by the IUCN, and due to their large numbers  populations are considered stable. However, some species only live in certain habitats, particularly wetlands, which are threatened by pollution or destruction.

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Photos

Large marsh horse fly (Tabanus autumnalis) by AJ Cann

Greenhead horse fly (Tabanus nigrovittatus) by Claudia Husseneder

A fly of the dead (Cynomya mortuorum) in Brussells, Belgium

image source: myself

Common name(s): crane fly, mosquito hawk, "big ass mosquito!" (inaccurate), leatherjackets (larvae only)

Scientific name: family Tipulidae

Can it hurt me?: No, despite looking like really big mosquitos, crane flies are not capable of biting you. In fact, many adults don't eat at all.

Can it hurt my plants?: There are a few species that can be agricultural pests at the larval stage. The larvae live underground and feed on the roots of some plants.

Should I kill it?: For most encounters? Nah, leave it be. I wouldn't even suggest trying to move it as they are extremely fragile and prone to losing limbs at the slightest touch. If you're a farmer dealing with an infestation of leatherjackets, make sure to follow pesticide protocol exactly.

You'll notice that unlike previous What Bug is This? posts, this one has a video rather than a picture. That's because in addition to their body shape, the front leg wiggling is an easy way to identify these flies. It's easier just to show it than to describe it.

Video from Bug of the Week

Common name(s): stilt-legged flies (not to be confused with stilt bugs or long-legged flies which are their own things)

Scientific name: family Micropezidae

Can it hurt me?: No

Can it hurt my plants?: No

Should I kill it?: No

Anything else I should know?: