The chocolate-brown raft spider inhabits bogs and ponds. It can be spotted sitting near the water, its legs touching the surface. When it feels the vibrations of potential prey, it rushes out to catch it, floating like a raft.
Statistics
Body length: 0.9-2.0cm
The raft spider is a large, chunky spider that lives around the edge of ponds and ditches, and on wet heaths and bogs. Adults sit at the edge of the water, or on floating vegetation, with their front legs resting on the water’s surface in order to feel for the vibrations of potential prey. Using the surface tension of the water, they chase out on to the water to catch their prey, which will even include tadpoles or small fish. Raft spiders will also swim underwater, often diving beneath the surface when threatened.
Are they dangerous? The fen raft spider is the UK’s largest spider, and one of the rarest. Despite its bite being poisonous and painful, it is not considered dangerous and would only lead to minor pain and swelling.
How to spot them: The fen raft spider has a dark body with cream stripes down the sides. The females are larger than the male.
Is the raft spider poisonous?
The fen raft spider is the UK’s largest spider, and one of the rarest. Despite its bite being poisonous and painful, it is not considered dangerous and would only lead to minor pain and swelling.
Are raft spiders aggressive?
Raft spiders have the unique ability to use floating objects as rafts and to walk on stagnant water. This aggressive spider feasts on all kinds of water-dwelling animals. Long fangs inject venom into victims, paralyzing them so the spider can drag them back to its “raft” to feed.
Habitat
The great raft spider, as with most other Dolomedes species, is a semi-aquatic spider. It inhabits lowland fen and grazing marsh areas and is dependent on the presence of standing or slow moving neutral to alkaline water. Within these areas it can be found on the margins of pools or ditches. Emergent vegetation is highly important for use as perches for hunting and basking and to support nursery webs. As a warmth loving species they avoid areas where water surfaces are shaded.
In dark swamps, survival can be a tough task. Raft spiders have the unique ability to use floating objects as rafts and to walk on stagnant water. This aggressive spider feasts on all kinds of water-dwelling animals. Long fangs inject venom into victims, paralyzing them so the spider can drag them back to its “raft” to feed.
Swamp Thing: This creature hunts on the surface of swamp water. The spider holds its legs wide and flat so it can walk on water without breaking the surface film.
Fang-Tooth: Curved, hollow fangs are attached at the ends of this creature’s large jaws. The raft spider injects venom into victims; the poison paralyzes them and dissolves their insides.
The raft spider got its name from its hunting technique of standing on a floating leaf and using sensitive feelers (called pedipalps) to detect prey. This creature uses the surface water of a swamp the same way other spiders use webs. Sensory hairs on the predator’s pedipalps feel vibrations in the water, such as a flying insect landing on the surface or small fish swimming nearby. Once the raft spider detects prey in the water, it darts across the surface, poisons its victim, then drags it back to its leaf to eat.
Lifeline: When this spider runs after prey, it leaves a trail of silk behind it. This way, if a victim struggles and drags the spider underwater, it can pull itself back above the surface.
Mating Code: During mating season, male raft spiders tap rhythmically on the water with their legs. This sends a special “code” to females, which follow the vibrations to the male’s location.
Trick Spider
- A raft spider sits on its makeshift raft and dangles its front legs in the water. The spider vibrates the tips of its legs to attract curious creatures.
- A newt sees the spider’s legs from below and thinks they might be potential prey, so it swims up to investigate. That’s when the raft spider springs its trap.
- The spider dips its first two pairs of legs into the water to grab the newt as it bites down on the victim and injects it with a double dose of paralyzing venom.
