Why a fly spike

In the 21st century, molecular methods play an increasing role in zoology, without them it is no longer possible to imagine modern systematics. I think that soon they will seriously squeeze the traditional ways to determine the species of the body. However, if classic entomologists completely die out - but the case is going on - then our grandchildren will not understand why a fly spike on their leg, and the tiger stripes on the skin, and indeed the tiger will not recognize. Still, the sequence of nucleotides is one genre, and bromine is the other. Both approaches will always remain needed, they do not cancel each other, but complement.

I will tell you about the benefits of "good old" methods on one example.

A few years ago, in Senegal, I happened to watch Hydrophorus Praecox (Lehmann, 1822) - the fly of the Dolichopodidae family. The name of the family has a stable Russian equivalent-flies-greenhouses, since most representatives of the family are characterized by a metallic green body color; However, there are many yellow greennuts, and the color of H. Praecox itself is metallic-gray. All greenfits are predators: they are very small invertebrates with food. Hydrophorus feeds mainly at the inherent larvae of small mosquitoes of the Chironomidae family (larvae of larger Chironomidae are known to fishermen and lovers of aquarium fish as a “moth”). The fly finds larvae in wet silt, and sometimes under water, where she immerses her head during the hunt. (Photo 1.)

Even representatives of the genus Hydrophorus are known for love to run on the surface film of water, as more noticeable bugs-waterproof bugs do. (Photo 2.)

Hydrophorus Praecox is an ordinary and very widespread look, it settled throughout the Eastern hemisphere from Scandinavia to New Zealand. How to distinguish H. Praecox from other types of Hydrophorus ?

When determining the species, entomologists are faced with problems that are well acquainted, for example, ornithologists: females are equally “gray”, and they are not easy, and sometimes impossible to distinguish from each other. It is much easier to distinguish males: a song helps in birds, in flies the structure of a copulative apparatus. In addition, males of many birds have brightly colored or elongated feathers, and in males of flies the shape and color of the legs are often modified; There are outgrowths, spikes, unusual bristles on the legs - all this greatly facilitates the definition. In males, H. Praecox at the end of the anterior lower leg has a characteristic bent spike directed inward [1]. (Photo 3.)

It is generally accepted that the modified legs of the males of flies are devices either to attract a female, or for the actual copulation, but the specific meaning of these devices is known only in a matter of cases [2]. Watching flies in nature and photographing them, I managed to find out why the males of H. Praecox need an apical spike on the front leg. The answer was very unexpected.

In the salt silt of the Estate of the Salum River in Senegal, this species turned out to be very numerous. It was noticeable that many flies jump in pairs: males are sitting on females, but actually mating was almost not observed. The “idle” males tried to drop happy rivals from females, but all the attempts that I watched were unsuccessful. (Photo 4.)

This behavior is not unique among insects. For example, it is characteristic of dragonflies, which also spend a long time in tandem. At the same time, the male holds the female with abdominal appendages by the neck, so as not to give in to the rivals. Several such tandems can be seen in the photo. (Photo 5.)

So, the male H. Praecox , having saddled the female, finds himself in a winning position: on the one hand, he can fertilize her, on the other hand, it is also not easy to discard him from the female as an infantryman to cope with the equestrian knight. But there is one difficulty: the female, albeit sad, can continue to eat her favorite larvae, but the male can not reach them. I was lucky to photograph how the males get out of the situation. You can’t call such behavior in knightly: waiting for the female to catch the larva, the male throws his body forward and steals the food in the female from his mouth. (Photo 6.)

And now let's carefully compare photos of 4 and 6. The male body on them is located in a completely different way, but the position of the end of the front leg in both cases is invariably: it remains opposite the rear body of the female, and the spike is inserted into the spare.

Thus, the function of the apical spike is clarified: it provides a hinge connection of the male with the female. Thanks to this, the male, on the one hand, is opposed by the attacks of other males, and on the other, it can move widely around the female: forward - for theft of food or backward - for copulation.

Dear readers, you will not succeed in engaging in molecular philosopheric geneticist, if only because it is an expensive pleasure. But everyone can replenish the growing ranks of classic entomologists - for this only love for nature, patience and attention are needed. And nature will generously reward for such an attitude to it.

Nikita Vikhrev,
cand. Biol. sciences, sotr. Zoological Museum of Moscow State University
Photo by the author

1. Grichanov I. Petersburg, 2006.

2. Sivinski J. Ornaments in the Diptera // Florida Entomologist. 1997. 80 (2). P. 142–164.