Assassins of the Insect kingdom

Whenever we hear the term ‘Robber Fly’, the first thing that come to our mind’s eye is a femme fatale or a vampiric version of the insectivora family, who sucks out the life-force of other insects, and sometimes from their own species too! Belonging to the Asilidae family of the Diptera order, the Robberfly is a curious case to study.

The adult Robber-flies emerge from the larval stage in hot summer months. We can see robber flies in singles, pairs while mating and waiting or capturing its prey. They prey on small flies, spiders, cicadas, butterflies. Butterflies are common prey as in this season butterflies are abundant

I was aware of this tendency of the robber-fly to prey on other species, but I had never expected it to catch and eat its own species. I saw this robber-fly pounce upon another big robber fly. I captured many photographs of it in action, but it was not at all disturbed by my continued presence. Within seconds it sucked its prey dry and finally, left its dry, crumpled husk of a body.

This Robber fly is from Order Diptera. These flies are easily distinguished from other insects because they have only one pair of normal wings. The second pair, just behind the first, is represented by two knobbed organs, the halters, used to stabilize the body during flight. Most flies have large compound eyes and mouth-parts that are modified for piercing, lapping or sucking fluids.

Worldwide there are 6727 species of robber flies known to us. Due to their predatory habits of feeding on other insects and their voracious appetites, they contribute to the maintenance of the natural balance among insect populations. To some extent, their targeted prey-base consists of plant feeding insects. The size of prey taken varies widely with each species of robber fly. Females also spend more time seeking prey than the males, possibly because of their reproductive requirements. Their general habit is to perch in open sunlit areas where they presumable command a good view of passing insects and then fly out to catch a suitable unsuspecting prey. Some robber flies take up station on exposed branches, others on the ground itself. Most species capture prey as it flies by, but some are known to capture prey that crawl on the ground.

Robber flies are swiftly flying predators with stout, spiny legs, a dense “beard” of bristles on the face. Like all robber flies, they capture their prey with their bristly legs and the prey is then injected with saliva containing neurotoxic enzymes, which rapidly immobilizes the prey and liquefy its tissues. In a relative short time the robber fly is able to suck out the dissolved tissues.

About the Author /

Yuwaraj Gurjar works with Raymond Limited - a renowned textile manufacturing company, but his love for nature always drives him to go places into wild India – being hugely diversified habitats. He has traveled across the country & Sri Lanka for nature observations and photography. His photographs have won many national and international awards; have been exhibited across the world. Some photos were included in field guides, educational websites and magazines. He actively spreads the awareness & knowledge about nature, wildlife & photography especially Macro Photography. He has developed a free Mobile App on Butterflies of Mumbai named “I love Butterflies”.

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