Fritz Vollrath.
A Close Relationship Between Two Spiders (Arachnida, Araneidae): Curimagua bayano Synecious on a Diplura Species.
Psyche 85:347-354, 1978.

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A CLOSE RELATIONSHIP BETWEEN TWO SPIDERS (ARACHNIDA, ARANEIDAE):
CURIMAGUA BA YANO SYNECIOUS
ON A DIPLURA SPECIES*
BY FRITZ VOLLRATH
Smithsonian Tropical Research Institute
P.O. Box 2072, Balboa, Canal Zone, Panama Spiders are known to be strictly carnivorous and, moreover, often cannibalistic as well. Yet some animals have achieved a status of close coexistence with several spiders, notably web spinners. Web-building spiders do not change web sites frequently. They are rather sedentary (Turnbull, 1964), which makes their webs a suitable habitat for associates. Some wasps (Eumenidae, for example) build their mud nests within the webs of the "social" spider Anelosimus eximius (Vollrath, in prep.) whose webs also harbor certain moth larvae (Robinson, 1977a) and Hemiptera (Vollrath, in prep.). The most striking examples of coexistence, however, are the kleptopara- sitic spiders of the genus Argyrodes (Theridiidae) that inhabit the snares of many web-building spiders (Brignoli, 1966; Robinson and Robinson, 1973; Vollrath, 1977).
In this article I describe some aspects of the biology of another spider that lives in close association with a web-building spider. It is the only spider known so far that is unable to capture its food but has to rely on its host to catch and, even further, to predigest the Prey.
CURIMAGUA AND DIPLURA
Curimagua bayano (Symphytognathidae; Forster and Platnick, 1977) has only been found riding on the cephalothorax and crawling on the webs of Diplura sp. (undescribed species of Mygalomorphae, specimen in the American Museum of Natural History) in Panama. Although the diplurid host is not uncommon in different localities in the monsoon forest at Pipeland Road (Canal Zone), only in the Bayano limestone cliffs (the stream banks of the Rio Maje and Rio Tigre) did their webs harbor Curimagua. On a recent trip to Iquitos, *Manuscript received by the editor January 15, 1979. Pu&e ÌöS:347-35 t 1978). http:llpsyche cnlclub orBig5Ìö5- html



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348 Psyche [December
Peru, I found a similar association between a Curimagua and a Diplura in the "white sand forest" of Mishana. Diplura sp. is a beautifully colored spider that measures up to 4 cm in length and builds sheet- or funnelwebs spreading up to 50 X 50 cm. The spider rests in the entrance of its retreat, a silken tube, waiting for prey to fall onto or crawl over the sheet. The prey is bitten in a sudden lunge and dragged into the retreat for consump- tion. In a few minutes the prey (e.g., a cricket) will be a mushy and liquified body, due to the combined action of the masticating movements of the relatively large chelicerae and the regurgitated digestive enzymes of the spider. Diplura's prey, as judged from the remains, seems to consist mainly of beetles (Coleoptera), crickets (Gryllidae), and ants (Hymenoptera). Millipedes (Diplopoda) and tailless whipscorpions (Amblypygi) were also found, as was a partly digested dendrobatid frog (Anura, Dendrobatas auratus). In contrast to the diplurid host, Curimagua bayano is a tiny, mitelike spider. The pale body of the adult female is globular and measures not more than 1.3 mm in length. The male is equally small; for exact measurements, see Forester and Plat nick (1 977). Curi- magua bavano was found in the retreats of several webs of Diplura. The highest number per host was three females and one male, all in the relatively small web (30 X 30 cm) of a male Diplura. An egg case which was also found in the host's retreat, and which was assumed to be of curimaguan origin, consisted of four small eggs incorpo- rated into a transparent and fluffy sphere (diameter 0.8 mm) of loosely spun silk. Curimagua crawls about between the silken threads of the host retreat, several centimeters behind the entrance, near the place where the host feeds. Because of its minute size, Curimagua has no difficulty in negotiating the fine mesh of silk. Often the animals were observed riding on the diplurid, perched on the center of its cephalothorax, apparently clinging to the fine hairs that cover it. Even their host's violent lunge for prey does not shake them off. I never saw the host react to Curimagua crawling about in the web or traversing the body of the host, even when it moved across the host's eyes (Figure 1). Diplura collected on Pipeline Road (where Curimauga was absent in ten Diplura webs inspected) also showed no hostile reaction when Curimagua climbed "aboard," suggesting that instead of being ignored the associate may not be perceived by its host.




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19781 Vollrath - Relationship Between Two Spiders 349 Figure 1.
The mygalomorph spider Diplura sp. in its silken retreat, feeding on a grasshopper. Perched on its eyes and on its chelicerae is the symphytognathid asso- ciate Curimagua bayano.
When I brushed Curimagua off the dipluran cephalothorax, they crawled about in the web and, as soon as contact was made with an extremity of the host, they started to climb it to regain their former position. During an experiment, a Curimagua female was taken from the back of a Diplura and confined to a Petri dish (diameter 5 cm) with another mygalomorph spider of approximately the same size as the diplurid. The Curimagua did nbt attempt to mount this spider.
Scanning photographs of a female Curimagua taken in frontal view of the "head" region (frontal ridge of cephalothorax: clypeus) show the distinct feature of this group, that is, the pedipalpal coxae lack the palpae (Figure 2). The coxae and the clypeus form a circular depression which is densely covered with fine hairs as well as trichobothria. The chelicerae - which in spiders are normally



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Psyche
[December
used to hold and kill prey - are tiny and fused at the bases (see also Forester and Platnick, 1977). Moreover, the chelicerae are located deep inside the mouthlike basin. Therefore, I consider it unlikely that they could be used to hold or tear even the smallest prey, thus restricting Curimagua to liquid food. I confined Curimagua to Petri dishes (diameter 5 cm) which contained a variety of small arthro- pods (Collembola, Coleoptera, Ricinulei) found in Diplura webs, as well as dead food items, but never did I find the spiders feeding on any of these offerings. Curimagua bayano shares fused chelicerae with its congenerics (Forster and Platnick, 1977), some of which construct very finely meshed orbicular webs with a diameter of only several mm (Eberhard, pers. comm.). The prey of these free-living congenerics are unknown. Their nets with a mesh size of approxi- mately 125 p (Patu saladito) may serve to filter for aerial plankton such as pollen and fungus spores (Vollrath, in prep.). When a Diplura that is carrying Curimagua bayano is fed an insect, the Curimagua climbs forward from its resting position on the central cephalothorax, over the eyes, and down the mighty chelicerae of its host until it reaches the digestive fluids enveloping the prey item. The abdomen of the pirating associate visibly swells and only a few minutes pass before the Curimagua climbs back onto the cephalothorax. Individuals moving about in the silk of the retreat are also attracted to a feeding Diplura, perhaps alerted by the vibrations generated by the masticating movements of the host. Curimagua is not the only associate of Diplura webs. Other spiders (Mysmenopsis ssp.; Platnick and Shadab, 1978) have been found by Kraus (1955) in Guatemala, and three species of Mys- menopsis (M. dipluroamigo, M. ischnamigo, and M..gamboa) were observed by Kirkendall (in prep.) in Panama in the webs of three differently sized diplurid spiders. These associates move about in the sheet region of the diplurid web, approaching and catching small insects that failed to attract the host. Some individuals might also move toward a feeding host, but I rarely saw them sharing its prey. Most often their approach is detected by the Diplura, which then turns around in the retreat, spreading silk with its long spinnerets and thus hindering the advance of the would-be pirates. I never observed this behavior of Diplura directed toward Curimagua. The



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19781 Vollrath - Relationship Between Two Spiders 35 1 Figure 2.
Scanning electron microscope photograph ( W X ) ot the Irontal cepha- lothorax of Curimquo bavano showing the two frontal eyes (El, the come and trochanier of legs !, the frontal ridge of the cephalothorax (the clypeus = Cly), the coxal processes (Cpx) of the pedipalpae with the reduced pedipalp (P), and, finally, the chelicerae (Ch) with the chelicerai claws (CO ability of Mysmenopsis dipluroamigo to survive without the "proper" host is shown by the fact that Kirkendall and I found a complex space web in a bush, resembling the web of the "social" spider Anelosimus eximius (Simon, 1892). This web (34 X 37 X 27 cm) contained 9 females, 10 subadult females, 16 males, 2 subadult males and 25 juvenile M. diphroamigo, in addition to 2 Ischnothele guianenesis (Walck.). Other associates of Dipfura webs encompass Coleoptera, dipteran larvae (Kirkendall, in prep.), lepidopteran larvae (Robinson, 1977), and therediid spiders of the genus Argy- rodes (Vollrath, 1977).




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352 Psyche [December
Curimagua bayano is an extreme case of specialization in spiders. It is the first spider described which is not a predator and not even a carnivore sensu strictu, but an ectoparasite or - in the terms of Robinson and Robinson (1977) - a dipsoparasite, resembling, in a way, representatives of another and most successful Arachnid order, the mites (Acarina) which produced many parasite genera (Vollrath, E., 1978). Curimagua bayano should not be called a commensal (Gray, 1967) since the fluids imbibed are either the host's costly digestive enzymes (5% protein solution in Tegenaria jtrica; Mommsen, 1977) or liquefied prey tissue. In both cases, Curimagua deprives its host of nutritive proteins, thus reducing its fitness.
My thanks go to Drs. H. Levi and N. Platnick for identification of the spiders, to Dr. R. Foelix for help with the scanning electron microscopy, and Drs. M. Robinson, D. Morrison, and D. Windsor for comments on the manuscript. Figure 1 was drawn by Arcadio Rodaniche after photographs and a specimen. The work was supported by a Noble Fellowship from the Smithsonian Tropical Research Institute.
REFERENCES
BRIGNOLI, P. M.
1966. La societa eterotipiche degli Araneidi 1. Rend. Acad. Naz. 16: 219-246. FORSTER, R. R. AND PLATNICK, N. I.
1977. A review of the spider family Syrnphytognathidae. Am. Mus. Nov. 2619: 1 -29.
GRAY, P.
1967. Dictionary of the Biological Sciences. Reinhold, New York. KRAUS, 0.
1955. Spinnen aus El Salvador. Abh. Senckenb. Naturf. Ges. 493: 31. MOMMSEN, T. P.
1977. Zusammensetzung und Funktion extraintestinaler Verdauungsfluessig- keit und Gift einer Spinne (Tegenaria atrica Koch). Dissertation, Univ. Freiburg.
PLATNICK, N. I. AND SHADAB, M. U.
1978.
A review of the spider genus Mysmenopsis. Am. Mus. Nov. 2661: 1-22.



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