Water boatmen were @SpeciesofUK from 14th
to 24th July, 2013.
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| Greater Water Boatman [Source: Flickr Creative Commons © JRxpo] |
In the UK, water boatmen are grouped into ‘lesser’ water boatmen (Corixidae and Pleidae species) and ‘greater’ water boatmen (Notonectidae). The simplest difference between the two is that lesser water boatmen swim on their front and greater on their back.[2]
Great water boatmen are also known as ‘backswimmers’
because they swim upside-down.
Greater water boatmen are called
backswimmers in the USA. It’s a name sometimes used here in the UK too, to
differentiate them from lesser water boatmen.
The most
well-known and common species of greater water boatmen is Notonecta glauca, the ‘common backswimmer.’[3]
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| Notonecta Glauca [Source: Wikimedia Commons © Factumquintus] |
N. glauca is widespread
throughout Europe and inhabits ponds, ditches and canals (still or slow-moving
water).[4] It has two
long legs which paddle like oars, making it look like a rowing boat.[5]
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| Notonecta Glauca in action [Source: Flickr Creative Commons © Katy Wrathall] |
N. glauca is greenish or brown.
Its eyes are reddish and large. The four front legs are short while the rear
two are very long.[6]
N. maculata is another greater
water boatman. It is distinguished by its brick-coloured forewings.[7]
And here is an example of yet another great water boatman species, N. obliqua:
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| Notonecta Obliqua [Source: Flickr Creative Commons © Drinker Moth] |
Greater water boatmen carry a bubble of
air with them underwater.
All aquatic bugs have to surface from time to time to breath oxygen,
limiting their time underwater. Greater water boatmen get around the problem by
carrying extra air in the form of a bubble attached to their body.
You can often see the greater water boatman's bubble of air because it
gives it a silvery appearance.[8]
Its ventral side is also covered in hairs which prevent water from
covering the spiracles that the greater water boatman uses to breathe.[9]
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| Greater Water Boatman reflection [Source: Flickr Creative Commons © Sam Dredge] |
Greater water boatman are carnivorous and
they punch above their weight.
Despite their small size, greater water boatmen prey on tadpoles, small
fish and other aquatic insects.[10]
Greater water boatman hunt by resting on the surface of the water
sensing vibrations. They immediately dive when they feel a disturbance.[11]
A greater water boatman will kill its prey by jabbing it with its
rostrum (feeding tube) and injecting its toxic saliva. They are very effective
predators.[12] The
bite from a Backswimmer can be even painful to humans as their saliva is toxic.[13]
Greater water boatmen can fly and will
move between different ponds, which helps to maintain genetic diversity in the
species.
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| Greater Water Boatman out of water [Source: Flickr Creative Commons © oktobrain] |
Greater water boatmen can fly when they become adults, allowing them to move to another pond.[14]
Greater water boatmen mate between December and May and eggs are laid between February and May of the following year, in aquatic plant stems.[15]
Here is a video of a greater water boatman clambering out of the water:
Lesser water boatmen are not actually
closely related to greater water boatmen.
Lesser water boatmen spend most of their time feeding on algae under
water.[16] In the UK, they make up
the family Corixidae, which includes
several hundred species worldwide.[17]
Lesser water boatmen are extremely common. Approximately half of the
species of water bug recorded from UK ponds are different kinds of lesser water
boatmen.[18]
The most common lesser water boatman in the UK is the widespread species
Corixa punctata.
C. punctata is found in most weedy ponds, lakes and slow-flowing rivers, but
rarely in water deeper than 2m.[19] They
thrive in water with neutral to high alkalinity, and are rarely seen in acidic
peaty streams and ponds.[20]
Like greater water boatmen, lesser
water boatmen carry a bubble of air they use for breathing. They brush it regularly
to access the oxygen.
C. punctata spend most of their
time at the bottom of the pond, anchored to the bottom or a plant.[21] If it loses grip it floats upwards then
suddenly rushes back down. They come to the surface only to renew their air
supply, hurrying upwards and collecting a new air bubble in less than a second.[22]
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| Corixa Punctata at bottom of pond [Source: Flickr Creative Commons © Wolfram Sondermann] |
C. punctata is brown, has long
hairy hind legs that it uses like paddles, slightly shorter middle legs and very
short front legs.[23]
C. punctata's front legs are
used to scoop up food. They are omnivorous but mainly eat algae and vegetable
matter.[24] Their
triangular heads have a straw-like mouthpart (a proboscis), which injects
plants with digestive saliva.[25]
Another remarkable talent of the lesser water boatman is its ability to fly with a ‘sprint start’ - rushing upwards through the water surface and straight into flight.[26]
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| Corixa Punctata close up [Source: Wikimedia Commons © Viridiflavus] |
Another remarkable talent of the lesser water boatman is its ability to fly with a ‘sprint start’ - rushing upwards through the water surface and straight into flight.[26]
Lesser water boatmen produce courtship ‘songs’
by rubbing body parts together.
In late spring courting begins. Male C.
punctatae attract females with a ‘courtship song’, rubbing their front legs
against a ridge on their head to make a low chirping noise.[27]
The loudest lesser water boatman, however, is M. scholtzi. It has the unusual talent of being able to ‘sing’ at
volumes of around eighty decibels by rubbing its penis against its abdomen. In
fact M. scholtzi was been recorded at
99.2 decibels, making it the loudest species on earth relative to body size.[28]
Female lesser water boatmen lay single eggs, which they attach to plant
stems or floating algae.[29]
Strange but true...
In Mexico water boatman are actually considered a delicacy, and are harvested and eaten in large numbers![30]
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