Water Boatman

Originally published in The Manitoban summer ?? 2011.

Ah – summer in Winnipeg; muggy heat we can't stand after 8 months of zero humidity and freakishly cold winter, freak storms, flooding, mosquitoess, canker worms, E. coli-infested eutrophic lakes – we love it all and by George we'll take it! This sweltering mid-summer issue I would like to tell you about a really cool bug. A bug you can respect: the Water Boatman.

The Water boatman belongs to the insect order Hemiptera, the true bugs (a cold virus is not a bug, a bacterial infection is not a bug, a fly is not a bug). Whether an insect is truly a bug depends on specific details of the wings and mouth parts, which are modified for piercing and sucking, oh my.

Water Boatmen are aquatic and have oar-shaped hind legs used for paddling. They typically inhabit lakes and ponds. These insects do not have gills and must breathe air from the water's surface; however, they frequently carry an air bubble with them during their lengthy underwater adventures and breathe oxygen from within the air bubble!

Over 500 species of water boatman have been identified, more than 100 of which are found in North America. Amazingly, one species in particular, Micronecta scholtzi, has just been credited as the loudest animal on earth! Water boatmen are only about 2.5 millimeters long and yet they create sound at volumes similar to that of a passing freight train or what you would hear sitting front row during a loud orchestra performance. This brain-boggling volume is produced during stridulation, sound produced by rubbing the differently sized ridges of two body parts together. In the case of the water boatman, stridulation is performed by rubbing the penis against the abdomen, which in a sense means the water boatman has the loudest penis in the world (hard to believe, I know).

A recent study by Sueur et al. (2011) reports a peak value of M. scholtzi calls at 100dB SPL (a log ratio between measured sound pressure level and a reference point defined by the threshold of audible hearing for humans). M. scholtzi thus has the highest ratio of dB (decibel) to body size ever recorded, making this water boatman the loudest animal on the planet!

Why do water boatmen need to be so loud? The song produced by stridulation is used to attract females. The males produce a three part song and it is the third part which is the loudest, meant to drown out the songs of competing males. Sueur et al. (2011) propose that the extreme volume achieved by M. scholtzi during stridulation may be the result of runaway sexual selection via intra-male competition.

The idea is this: females localize the acoustic signals produced by loud males more easily than those of quieter males whose songs are masked by the loudest males. Typically, there is a balance between signal volume (high volume = more females) and predation (higher volume = more predators) but in this case, it is possible that the water boatmen either have no predators that use acoustics to find prey or the boatmen are so effectively able to evade these predators that the volume of their signal is not regulated by the negative selection pressure normally imposed by predation (Sueur et al. 2011). In short, the male with the loudest penis gets the most females. 'Nuff said.