This unfortunate lesser boatman was attacked by the larvae of a watermite, some days before this picture was made. The larvae attached themselves with their special mouthparts to the legs of their host, after that they went in to the immobile protonymph or nymphophane stage, looking like little, teardrop shaped sacs. At the spot were a larva drilled its mouthparts in the exoskeleton of the insect, a little "suction channel" is formed. Through this channel, the stylostoma, blood and body fluid is sucked from the host. The protonymphs rapidly get taller in this way and through the outer skin the nest stage of the watermites, the nymphs, are visible. (I do not know the species name of the insect, or that of the watermite).

Of course the lesser boatman is weakened by its parasites - and when there are many as on this photo, it's worse. The loss of protein can be so severe the insect perishes. The protonymphs that are not full grown, will die too. When there not too many, the host may survive. With the voluminous sacs on its legs swimming is almost impossible and the reverse posture as on the picture is never seen with healthy specimen.

In one of the protonymphs the (deuto)nymph is almost developed and clearly visible. It may hatch within a few days. The nymph is a predator and takes the same food as the adult. After some days the nymph of some species attach to a waterplant with its legs or chelicerae and rests in a new motionless stage, called the teleiophane stage or the tritonymph. Inside the tritonymph the adult watermite develops and hatches by tearing open the skin.