Rhantus suturalis
THIS BEETLE IS WORLDWIDE VERY COMMON IN LITTLE POOLS THAT DRY OUT
DURING SUMMER.
Rhantus suturalis
with air bubble
Those pools are also the breeding places of mosquito larvae - the preferred food of this
beetle. As the beetle also often visits garden pools, that means less mosquito bites for us! The
specimen of these photos had landed in a fish tank that was standing in my garden. And it must have
laid a few eggs there, because some days later suddenly I saw it's little
larvae.
The beetles of the genus
Rhantus are medium sized, apparently dark brown beetles which are,
like all diving beetles, excellent swimmers. They can also fly very well, and so easily escape from
a pool which is drying out and migrate to another. With a closer look at
Rhantus suturalis
the dense black punctuation of the elytra is visible, this punctuation on a golden yellow base gives
the dark brown impression when seen from a normal distance. Older names (synonyms) for this beetle
reflect this punctuation:
Rhantus pulverosus and
Rhantus punctatus. The
beetle has a light yellow coloured margin. Just like all members of the diving beetles family
(
Dytiscidae) this beetle keeps a supply of air under its elytra, that is refreshed by
protruding the tip of the abdomen above the water surface. When under water the insect now and then
presses the air from under the elytra into a relatively large air bubble, that is held at the tip of
the abdomen. By diffusion oxygen in the water will migrate in this bubble. After some time the
beetle sucks the refreshed air bubble back in by enlarging the space between its abdomen and elytra.
In this manner the air supply is longer usable, and the bubble is what is called a
physical
gill. The beetle shows this behaviour more when it wants to hide and remain longer under water.
Sometimes the bubble is the only thing that is revealed of the hidden insect.
Rhantus suturalis aspirating
Rhantus exsoletus
Small pools with mosquito larvae can be found almost at any place on the world, and the same
goes for the beetles of the
Rhantus genus. There are a number of species in Europe, a few are
very common.
Rhantus suturalis, a worldwide spread species, is recognisable by a
rhombus-shaped dot on the neck shield. At the right:
Rhantus exsoletus, another very common
species that has a vague-black margin at the end of the neck shield instead of a rhombus-shaped dot.
At the under side this beetle is not totally black like
suturalis, but yellow. Please notice
the (not specific) differences in the spots on the heads.
On the pictures at right the two species are presented. (R.
suturalis is resting
horizontally on the bottom, while R.
exsoletus sits vertically on a leaf.) In a superficial
glance the beetles look the same. It's a pity the position of the heads is different on the two
pictures, this makes comparison more difficult. As is shown on the picture under, R.
suturalis has a black under side where R.
exsoletus is more yellow.
back to: WATERBEETLES 1
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Rhantus suturalis
COPYRIGHT:
All pictures on this site were made by
Gerard Visser (Aadorp,
Netherlands), unless stated otherwise. All rights remain with him. These pictures may not be used
for purposes any other than private viewing or printing. Do NOT hardlink to these pictures or
place them on other websites without the author's approval. Should you need them for purposes
which include third parties, you must ask the author permission by
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educative material are much encouraged to do so, after approval as mentioned and giving the normal
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© G.H. Visser 24-08-2007
rev. 27-10-2007
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