Spiders and harvestmen as gastropod predators

Abstract

Abstract. 1. Reports are reviewed of gastropod feeding (malacophagy) by spiders and harvestmen. Although the standard textbooks on arachnids recognise the importance of gastropods as prey of harvestmen, none apparently refers to malacophagy by spiders. A review of several hundred papers on spider feeding habits revealed that species from several families kill and devour slugs and snails in the laboratory and/or ®eld.2. Malacophagy has been reported most frequently among mygalomorph spiders, and can make up a substantial proportion of the diets of some species, however gastropods make up an insigni®cant percentage of the prey of most araneomorph spiders. The spiders that eat gastropods are species with broad diets composed predominantly of arthropod prey. No species of spider appears to feed exclusively on gastropod prey.3. Harvestmen from several families have broad diets that often include gastropods. Several species of the family Trogulidae and at least one species of the family Ischyropsalididae [Ischyropsalis hellwigi (Panzer)] are specialised gastropod predators. The trogulids are slender animals that attack the snail through the shell aperture (shell intruders). Ischyropsalis hellwigi, on the other hand, can crush snail shells with its powerful chelicerae (shell breakers).4. The review highlights apparent convergent evolution by harvestmen and Carabidae of two mutually exclusive morphologies found among gastropod predators. It also suggests that there is an urgent need for systematic studies to be conducted to establish the extent and ecological importance of malacophagy in natural and anthropogenically altered habitats.

Hesperonemastoma Smilax, N. SP., A Remarkable New Harvestman from a Cave in West Virginia, with Comments on other Reported Cave-Dwelling Hesperonemastoma Species (Opiliones, Ischyropsalidoidea, Sabaconidae)

“…Within Sabaconidae, the morphology of Hesperonemastoma is extremely divergent. It should be noted, however, that convergence of general body habitus is well known in Opiliones; Taracus itself (Sabaconidae), Ischyropsalis (Ischyropsalididae), Nipponopsalis (Trogulidae), and Megalopsalis (Monoscutidae) all resemble one another despite all belonging to separate families and even suborders, perhaps because of a common adaptation for feeding on snails (Nyffeler and Symondson, 2001) or, in the case of the monoscutid, secondary sexual characters of the males. It now seems that the striking similarity of Hesperonemastoma, Crosbycus, and several genera of Nemastomatidae is also the result of convergence or parallelism.…”

An enigmatic spiny harvestman from Baltic amber

“…These are also distinctive harvestmen with long and spiny chelicerae. Ischyropsalis hellwigi is known to be a specialist predator on gastropods and the especially enlarged and powerful mouthparts are used here to crack snail shells (Martens 1965;Nyffeler & Symondson 2001). The diets of other Ischyropsalis species are not well known.…”

The detection and decay of Cry1Ab Bt-endotoxins within non-target slugs,Deroceras reticulatum(Mollusca: Pulmonata), following consumption of transgenic corn

“…Due to their pest status and diverse feeding habits, slugs, such as D. reticulatum , have been widely studied and form a significant proportion of the diet of many generalist invertebrate predators, such as carabids and spiders (Symondson et al , 2002Nyffeler & Symondson 2001;Harper et al 2005). It is the abundance of slugs in corn fields (Rollo & Ellis 1974;Byers & Calvin 1994;Hammond et al 1999) that increases the likelihood of transferring Cry1Ab-endotoxins from transgenic corn to their natural enemies higher up the food chain.…”

“…This is particularly important given the slow degradation rates of Bt-endotoxin in plant material during the autumn, winter and spring (Zwahlen et al 2003b) and although D. reticulatum shows preference for fresh plant material (Lutman 1978), their diet from arable crops is particularly diverse (Hunter 1968). Similarly, earthworms constitute an important part of the diet of many of these invertebrate generalist predators Nyffeler & Symondson 2001;Harper et al 2005). Potentially, this further exposes natural enemies to increased transgenic toxins if they are not rapidly broken down.…”