You can be lucky sometimes! I had read about the insects commonly called “mantis-flies” and seen many images of them, but I had never seen a live one in the flesh. We were at dinner with neighbours one night when one landed by my plate of food – no kidding. Pandemonium ensued as I tried to catch it, shouting for a container of some kind. Finally it was corralled and I had one to photograph. Here it is! (below)
But what is a “mantis-fly”? Is it a mantis or a fly? Neither actually. It’s a type of lacewing and is therefore a member of the order Neuroptera. Mantis-flies are members of the family Mantispidae within that order. They may be known by several other common names like mantidflies, mantispids or mantid lacewings. Confused? Which is the correct term? I would plug for “mantispids” because this reflects their family name.
We have about 45 species of mantispids in Australia. Adult mantispids have distinctive mantid-like raptorial forelegs and two pairs of lacy wings. Adults of some species are up to 25mm in length, although the one pictured is half that length. Another distinctive feature of mantispids is how the first segment of the thorax (the pronotum) is very elongated, appearing like a long ‘neck’.
Adult mantis-flies are predators of small insects such as flies, using their raptorial forelegs to catch prey. The larvae of the mantispids which occur in Australia are parasites of spiders! Here’s how it works. Female mantispids lay large batches of small stalked eggs, often hundreds at a time. Hatching larvae either search for a spider egg sac and burrow in, or climb aboard a female spider and enter the egg sac as it is constructed, to feed on the spider eggs. Larvae that climb aboard female spiders may feed on spider blood while waiting for the egg sac to be produced. If the larva boards an immature spider it can put its own development on hold (a process known as diapause) until the spider moults into a mature female.
There are three larval instars in mantispid life cycles. The second and third instars are quite sedentary compared to the mobile first instar larva. Pupation occurs within the spider egg sac once all spider eggs are consumed. Emerging adults vary considerably in size depending on the number of spider eggs eaten as larvae. Some mantispid species go through an elaborate courtship prior to mating which includes sparring with their raptorial forelegs. Some common species may be drawn to lights at night, while others may be seen ambushing prey on flowers.