It comes out at sunset, scurries along the banks wriggling its long snout, dives into the pond to fish for small larvae. Discreet, the Crossope passes unnoticed.
The shrews, a large family
If we know the common shrew, small but great ally of the gardener, its semi-aquatic cousin, the Crossope, remains unknown. Frequent host of rivers, watercress beds, ponds and ditches, Neomys fodiens belongs to the same family, the Soricidae. It shows the same pointed, mobile snout, with long whiskers; its coat is rather grayish to black, with a well marked white belly. Of beautiful size, it measures up to 10 cm, without forgetting the tail, that is 8 cm more! This makes it the largest of the dozen shrews present in France.
An insatiable insectivore
The aquatic shrew comes out at sunset and is active all night long, looking for preys, mainly small invertebrates. On the menu: underwater, aquatic insect larvae, crustaceans, fry; on land, beetles, snails, worms, and even amphibians and small mammals. If its sight is weak, its sense of smell and hearing are excellent. Reinforced by mobile vibrissae, real underwater detectors. Its preys thus located, it seizes them with its small red and pointed teeth, poisons them by the toxic juices of its salivary glands. This is an efficient strategy, allowing this small mammal with high energy expenditure to be fed in abundance.
An accomplished swimmer
Water is its element, the aquatic shrew never goes too far from it. If it trots on the banks, it regularly dives with ease, swims between two waters, circulates on the bottom, goes up and floats like a cork.
It is nicknamed the "frame shrew". Its hind feet are lined with stiff hairs, reinforcing its support. Its tail is also equipped with two rows of the same hairs, and plays a powerful propelling role. Its coat is perfectly water repellent, and to complete the equipment, its auditory holes are obturable. An accomplished swimmer that will dig its burrow on the banks to house its young.
Many young
From April onwards, Crossopes are concerned about their offspring. Males and females meet each other, sometimes a little harshly. Through a small hole of 2 cm in diameter, the female will enter her carefully dug burrow. She will line it with plants rolled into a ball to accommodate 6 young on average. Her gestation will have lasted 2 weeks, 3 at the most. The reproduction will take place until September, the peak of the births being in May-June. The young will become adults after a few months and will reproduce in general the second year.
They will live at best 2 years. Mortality in the aquatic shrew is important, in the young as well as in the adults, especially during the breeding season.
Light traces
Discreet, nocturnal or crepuscular, the Crossope is difficult to see. Minute traces let us guess its passage. The fine and humid mud of the banks will be marked with light prints, with five fingers, without webbing. The posterior foot will measure hardly 1 to 1,5 cm, the anterior one will be even smaller. The droppings are almost invisible: 5 mm long, for 2 mm of diameter. Tiny droppings can be seen... Occasionally some remains of meals are observed, shells of snails, cases of caddisfly larvae, or better a larder supplied with preys half consumed. Other indication of presence, small acute nocturnal cries...
Small discreet mammal, the aquatic shrew plays an essential role in the aquatic ecosystems. But the degradation of its habitats is beginning to impact its populations, on the IUCN lists it is classified as a species of minor concern on the whole French territory, but in some departments the species is becoming almost threatened, vulnerable, even endangered.
