While in Costa Rica we were visited by this beast (see photo). It was about the size of a cigarette packet, could fly (but not very well), and dogs seemed nervous of it. We haven鈥檛 managed to identify it and neither could locals or tour guides. We鈥檙e not even sure what sort of insect it is. Can any of your readers help?
鈥� The insect in the picture is a male , which is in the order Megaloptera and the genus Corydalus. However, a species identification is not possible without the full insect being visible.
Dobsonfly larvae inhabit fresh running watercourses before crawling out and hatching into the adult shown. The genus Corydalus attracts attention throughout both north and south America as a result of its size 鈥� its wingspan can reach 16 centimetres. The males possess very large mandibles, as shown in the photograph, which can be up to 3 centimetres long. They are too long to be a threat to humans, though, as the leverage is too poor to puncture the skin.
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鈥淲hile male dobsonflies have mandibles that are 3 centimetres long, they pose no threat to humans鈥�
Dobsonflies are nocturnal but, like other insects, are attracted to lights, which is probably what attracted this specimen to you. The dogs were most likely bothered by the sight of a large insect fluttering around them.
If you had asked a fisherman to help identify the insect you may have had more luck. They tend to have an in-depth knowledge of local insects as they make similar-looking fly hooks to help catch fish.
Peter Scott, School of Life Sciences, University of Sussex, Brighton, East Sussex, UK
鈥� The insect is a dobsonfly and part of the Megaloptera order, which also includes the alderflies and fish flies. The individual shown is almost certainly a species of Corydalus and its large jaws indicate that it is a male.
Males use their jaws in mating displays and in threat postures directed at rival males, as well as to grasp females during mating. They have little leverage, though, so are not as fearsome as they may seem to the human observer. In contrast, the female鈥檚 short, pincer-like jaws can inflict a painful nip.
Dobsonflies spend most of their lives as aquatic larvae, hiding under stones and pouncing out at prey. Some fishermen, who use North American species as bait, call the larvae hellgrammites. The larger species can take several years to mature. When mature, the insect can eject a foul-smelling, and no doubt foul-tasting, secretion from the anus as a deterrent to predators. The adults are short-lived and do not feed.
The larger species of dobsonfly can have a body length of 12.5 centimetres, with males having jaws up to 2.5 centimetres long. There are 30 species of Corydalus, found mainly in Central and South America. Three occur in North America, the most common being Corydalus cornuta.
Chris O鈥橳oole, Hope Entomological Collections, Oxford University Museum of Natural History, UK