HOMEPAGE

Walking on the water

Biology and captive breeding of giant fishing spider Ancylometes

By Francesco Tomasinelli: giantsquid@tiscalinet.it

UPDATED 3/12/2003

Introduction

Probably some of you have seen some amazing movie of a spider fishing. It dives underwater to capture a small fish with incredible skill. Spiders like this belong to the family Pisauridae ( nursery web and fishing spiders ) closely related to Lycosidae ( wolf spiders ) and Ctenidae ( wandering spiders ), counting about 500 different species from all over the world. The famous genus Pisaura and Dolomedes, the so-called raft or fishing spiders, very similar in morphology and habits to bigger Ancylometes are included in this family. As mentioned nursery web spiders are related to famous wolf spiders but several differences in anatomy and behaviour exist. The eight eyes are not grouped in a square formation and are smaller. They carry the egg sac with the jaws and mother spins the nursery web for the spiderlings. Pisauridae usually have longer legs too, slightly different carapace and abdomen. In wolf spiders the egg sac is attached to the spinnerets and after hatching the young’s climb on mother’s back to carried around for some week.

The genus Ancylometes contains 15 species at the moment counting some of the largest araneomorph spiders, like the A. rufus depicted here: adult females measure 4-5 cm in body and more than 10-12 cm as legspan; the males are smaller, with about 2,5-3 cm body but with longer legs. Both are brown with dark spots on the abdomen. Males have two thin clear lines all along the carapace, very evident palps and longer legs. Juveniles are pretty similar to adults but external sex determination is sure only in the last moults when patterns on carapace, abdomen and palps shape become visible.

Habits and captive care

They live near ponds and small lakes in tropical rainforest of South America. I have seen they almost always stay in close proximity of water, most of the times with legs stretched over the surface. Young’s can walk on the water surface with impressive speed and agility. During this action their locomotion is changed and adapted to the environment, they seem to row, like water runner insects (Gerris). They are able to walk on water because of the fine hairs on their tarsi, which wrap air and act like small buoys. They are terrestrial and unable to climb on glass and very smooth surfaces and normally do not wander on vegetation and branches (but of course you should use some cover for the terrarium). Ventilation is not so important but several hole should be made. Always keep an eye on water and humidity. Never let the enclosure to dry out.
Ideal temperature range is around 25 C with lots of humidity but they can easily tolerate some fluctuation.

They hunt using wait and rush tactics like other “hunting spiders” As mentioned water is not an obstacle, even if full-grown specimens will break the surface easily. The eyesight is average; they can see big moving object and but their perception is worst than in wolf spider. Probably they can give a painful bite but without any consequence. I have never being bitten and have read they are not dangerous. You can feed them with insects, but they also like small frogs and lizards, both natural prey items in their habitat. Sometimes, if hungry, they take tenebrionid coleopterans also, like the adult of the popular mealworm (Tenebrio molitor). Earthworms are a good choice also, given their relation with humidity.
’m sure most of you are wondering if they are able to take fishes like our Dolomedes fimbriatus. Even if bigger specimens are less prone to dive the are able to capture small water creatures that are consumed entirely on the ground. It’s advisable to employ fishes smaller than the spider. Young's seem to have a better capabilities to seize fishes.

Probably one of their most surprising feature is their amazing ability to dive underwater for more than an hour when threatened. They can remain so, on the bottom of the pond, grasped to water plants or branches. Small air bubbles are trapped in hairs surroundings the book lungs which allows the spider to breathe for long periods under water.

For all those reasons I think it’s more interesting to build a small terra-aquarium to enjoy the Ancylometes. For example, you can provide an adult female with 25cm X 35cm X 25 cm terrarium with a small pond inside, about 5cm deep and 20-30% of the surface. You can just build a small pool with glass and silycone as visible in the picture here. It’s advisable to put some branch near the water to facilitate spider movement in the area. It’s even better if you add some plant, like a small bromeliad, Pothos or fern ( even a good plastic copy will work), lots of moss near the pool and bark chips.

Mating is another interesting point about this species. As always both should be well fed and female kept in the terrarium for some week. The male is quite prudent but will come close to the female following the trip lines with pheromone she has laid. After some brief touch she seems to fall “in trance”and then the male climbs over her and immobilise the mate using silk! It’s one of the rare cases of bridal bondage. Some crab spiders – Thomisidae – have this habit also. The male is extremely quick and skilled and in a matter of seconds a thick white layer blocks her legs; she offers no resistance. With the female neutralised he can at last mate in the usual “hunting spiders position” the male hugging the female from above. The copulation lasts less than a minute. After mating he will be very nervous and will try to put as much distance he can between himself and her. In the meantime the female will break free of the silk.

In the following days she will be very hungry and after about a week will produce a cocoon. This process is quite complex and some device should be taken to prevent failure. I strongly advice to give her lot of food before mating and eggcase construction to prevent excessive weakness (like in some teraphosidae). She needs some kind of frame also. Fern leaves and a few branches, suspended 3-4 cm above the ground will be enough.

The cocoon is quite big and is soon covered with a liquid secreted by her mouth. It makes the eggcase waterproof and has probably anti-fungi properties. It’s carried with the fangs and never left. During this time the spider won’t eat anything.

After about a month, right before hatching, the female build the famous nursery web, about 10 cm in diameter and suspended above the ground. The egg case contains 100-200 young’s with 2 mm body.

They spread on the web and make their first moult within two days. The mother can be quite aggressive during this time and she is quite protective of her young’s. They stay together for a while but after some days disperse, start feeding and initiate independent existence. Spiderlings mature in about 10-12 months and are very cannibalistic. They won’t loose any occasion to eat each other’s, especially if different sizes are present. Do not keep them together if you can. If you must, give them a small pond with some water, a very wet substrate, and lots of fruit flies or micro crickets. After some moult is always better to separate them or cannibalistic losses will grow too much. Just keep them in small containers with very wet irish peat moss substrate and a small bark piece (see pic). Humidity is very important: they can survive just a few hours in dry environment.

You can expect up to three cocoons are made, number varying in relation to animal size and feeding. After a successful reproduction most specimens die, especially males, that can live just 14-16 months. The females have better longevity, up tp two years or more.

Further reading:

http://naturkundemuseum-karlsruhe.de/ancylo.htm. A small page with the last informations on recognized species of Ancylometes


Many Thanks to Witold Lapinski for his precious advices about identification of specimens and to Emanuele Biggi and Matteo Dei for their help while taking pictures.