2Universität Regensburg
Naturwissenschftl. Fakultät III Biologie

Institut für Zoologie, Universitätsstr. 31
93053-Regensburg, Germany

Spiders of the genus Argyrodes Simon 1864 (family Theridiidae, cobweb spiders) live almost exclusively in the webs of other spiders. Argyrodes species may interact with their hosts in several ways, as a kleptoparasite stealing the hostís prey, as a host predator, web-stealer or commensal (see Cangialosi 1997 for discussion). Many Argyrodes species occur in the tropics and subtropics. They are often found in webs of various species of the genera Argiope Audouin 1826 (Araneidae), Nephila Leach 1815 (Tetragnathidae), Agelenopsis Giebel 1869 (Agelenidae), Neriene Blackwall 1833 (Linyphiidae) and Achaearanea Strand 1929 (Theridiidae; see Exline & Levi 1962).

In the course of behavioral studies on a Floridian endemic spider, the red widow Latrodectus bishopi Kaston 1938 (Theridiidae; Marion County, Ocala National Forest, along Hwy 40, 1/4 mile west of Central Lookout Tower) three different species of Argyrodes were collected from their hostsí webs. Latrodectus bishopi, limited to Central and South Florida (Kaston 1970; Levi & Levi 1990), builds its web on palmetto shrubs (Genus Sabal) in oak scrub-sand pine woods. The base of the web consists of a large, dense, slightly convex sheet, with an extensive three-dimensional large-meshed network of threads above the sheet and a densely woven, funnel-shaped retreat attached to the convex sheet. The retreat is always placed in an unopened palmetto leaf, with the opening of the retreat funnel directed upwards. During the six-week observation period (July and August) the red widow spiders spent most of their daytime hours in the retreat. Daily, 51 websites of young, subadult and adult female and male L. bishopi webs were monitored. All Argyrodes specimens were found only on webs of adult or subadult female L. bishopi, never in the webs of males or very young widow specimens. Argyrodes was always found in the large-meshed network above the convex sheet, never in the retreat or the convex sheet. The following three species of Argyrodes were found in L. bishopi webs at the above mentioned location: Argyrodes elevatus Taczanowski 1872; Argyrodes furcatus (O. P.-Cambridge 1898); Argyrodes caudatus (Taczanowski 1873), see Table 1. The Argyrodes species composition on individual L. bishopi webs was not recorded.

On August 12 and 13 all 51 L. bishopi websites were checked for Argyrodes specimens. On August 12, fifteen webs were found to carry Argyrodes specimens and all Argyrodes specimens were collected. Twenty-four hours later, the same L. bishopi webs were monitored again; eleven of the fifteen webs had Argyrodes specimens. Within 24 hours, the population of A. furcatus was restored to 50% of the original number. Possible Argyrodes recruitment sites (webs of other potential hosts) were not investigated. Distances between owner-occupied L. bishopi webs ranged from 2.1m to 10.8m; distances between Argyrodes-invaded widow webs ranged from 2.1m to 8.4m. The observations in the present note suggest that webs of other spider species living in close proximity to L. bishopi webs may also harbor Argyrodes specimens and that movements between these different host webs may occur.

On 26 July 1997 an adult female of A. furcatus was collected while feeding on a dead juvenile L. bishopi. Whether A. furcatus had caught the widow host or was just feeding on a dead host spider could not be determined. During the six-week observation period, prey capture and courtship behavior between Argyrodes males and females were observed frequently. Argyrodes specimens were found to reside in empty L. bishopi webs, but they were never observed in host-free webs built by a different species than L. bishopi on the palmetto shrubs.

Table 1. Collection dates, number of collected Argyrodes specimens and gender distribution.

Date
A. elevatus
A. furcatus
A. caudatus
17 Jul 1997
1?, 2/
4?, 3/
2?, 2/
31 Jul 1997
ó
4?, 28/
1?, 1?juv, 2/
12 Aug 19971
1?, 1/
13?, 30/
3?, 1?juv, 3/
13 Aug 19972
ó
6?, 15/
1?, 1/

1Collected in 15 L. bishopi webs.

2 Collected in 11 L. bishopi webs.

Egg sacs of A. furcatus were collected with adult females and are described here for the first time. Single light-brown spindle-shaped egg sacs hang from thick silk threads in the three-dimensional network of the widow web. The egg sac ends with a round silk collar, and is very similar to the egg sac of western A. baboquivari as figured by Exline & Levi (1962: fig. 2).

Several aspects of the relationship between Argyrodes and its hosts, e.g., host-specificity, territoriality among various Argyrodes species, movement of Argyrodes invaders among host webs of the same or of different species and others can be investigated conveniently at the described location. Argyrodes and Latrodectus voucher specimens are deposited at the Field Museum.

We are grateful to K. Cangialosi and E. Leigthon for critical reviews of the manuscript. Mr. J. Thorsen, District Ranger in Ocala National Forest gave permission to observe red widows and to collect voucher material.

Summary

Specimens of Argyrodes elevatus, Argyrodes furcatus, and Argyrodes caudatus were found in the three-dimensional large-meshed network above the convex sheet in large webs of subadult and adult females of the Floridian red widow, Latrodectus bishopi. The egg sac of A. furcatus is described for the first time. Argyrodes specimens were also observed eating their host and remaining in empty host webs during the six-week observation period.

References Cited

Cangialosi, K. R. 1997. Foraging versatility and the influence of host availability in Argyrodes trigonum (Araneae, Theridiidae). Journ. Arachn. 25(2): 182-193.

Court, D. J. 1971. The behaviour and web structure of the Katipo, Latrodectus katipo. Tane (The Journal of the Auckland University Field Club) 17: 149-157.

Exline, H., and H. W. Levi. 1962. American spiders of the genus Argyrodes (Araneae Theridiidae). Bull. Mus. Comp. Zool. Harvard College Vol. 127(2): 75-204.

Kaston, B. J. 1970. Comparative Biology of American Black Widow Spiders. Trans. San Diego Soc. Nat. Hist. 16(3): 33-82.

Levi, H., and L. Levi. 1990. Spiders and their kin. Golden Press. New York. Western Publishing Company, Inc. Racine, Wisconsin.