Apr 16, 2025
Water measurers - Hydrometra stagnorum - out on the water in full sun. They look quite like stick insects, but are more closely related to shield bugs and pond skaters.
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Water measurers - Hydrometra stagnorum - out on the water in full sun. They look quite like stick insects, but are more closely related to shield bugs and pond skaters.
#1836 - Hydrometra sp. - Marsh Treader
AKA Water Measurer.
The Hydrometridae are a new family for me - I don’t recall ever hearing of them before, let alone actually see one. Very weirdly shaped heads.
Most of the 147 known species of Hydrometrid are tropical, and wingless, but this one clearly has fully developed wings, which may explain why I spotted it on my windscreen instead of on the surface of the water near the edge of a marsh. It may have mistaken the reflection off the glass for water, which happens to a lot of aquatic insects that also fly from pond to pond.
Like most insects that live on the surface of the water (which includes families closely related to the Hydrometridae) they’re predators of unlucky insects stuck in the meniscus, but can also use their barbed rostrum to snag prey from under the surface.
HD image Source: Flickr
My first time seeing hydrometra! This was from a routine OHE on a rabbit. Hydrometra is water in the uterus.
Water measurer (Hydrometra stagnorum)
This long-legged insect is found on the water or near the water’s edge in ponds, ditches and slow running streams. As other insects moving on the water surface, it has hydrophobic hairs on its legs. Unlike most other insects with the same choice in habitat though, the water measurer is a slow animal.
Its mouth parts are shaped as a needle which is turned up under its head when not hunting. It feeds off small insects and larvae that either end up on the water surface by accident or emerges to get air. It’ll often stand on the water and wait for the chance to impale a mosquito larvae on its needle-like mouth.
It itself will fall prey to birds, other insect and spiders that also use the water surface as their hunting ground. This is where its unremarkable colouring and slow movements come into play. It is virtually invisible when standing still, both from above and from the sides.
This animal was found in a stream in the woods.