Stiletto fly

If you were a small insect you wouldn't want to meet the Northern Silver-stiletto fly (Spiriverpa lunulata) while out strolling on the river bank.

The white eel-like larva of the fly lives just under the soil surface. It detects the vibrations of something walking on the surface; stealthily it wriggles to beneath its unaware prey, before piercing them from below with its sharp mouthparts, injecting poison that leads to instant paralysis. Finally it deftly drags its prey out of sight beneath the soil. It all happens so quickly it's a case of now you see it, now you don’t. The ultimate sci-fi horror monster, fortunately it's only a couple of centimetres long.

Watch where you tread: the larva of the Stiletto fly lies in wait for prey beneath the soil

In Britain there are 14 species of stiletto fly. Some have silver males but mostly they are brown in colour. Most species are very habitat specific, especially where loose sand is present as on sand dunes and beside rivers. Only one species is very widespread, with the others mainly nationally scarce, rare or endangered. Hence such flies can be important in site evaluation and decisions over site management.

The Northern Silver-stiletto fly lives on Exposed Riverine Sediment - pebbles and gravels found at the river's edge, a habitat of great importance for its invertebrate life. This extraordinary species is protected on the Biodiversity Action Plan, and Buglife is currently working to conserve both the fly and its habitat.