A Florissant fossil spider discovery

The Florissant Fossil Beds National Monument is known worldwide for its late Eocene (34mya) fossil plants and insects. Recently, a fossil spider was discovered at the commercial quarry, which is near the fossil beds (Fig. 1). Due to the condition of the fossil, it can only be assigned to the family Lycosidae (see table) (Rasnitsyn, 2012). If correct, this classification would make it a wolf spider.

This fossil wolf spider lived 34mya under Florissant rocks, within the forest litter or on short herbaceous plants (Meyer, 2003). Based on its modern relatives, it would have had colours that helped camouflage it, allowing it to hide from its prey (Meyer, 2003). According to the Florissant Fossil Beds National Monument fossil database, only one other member of the family Lycosidae (from the Greek word for ‘wolf’) has been discovered there. Petrunkevitch (1922) described this fossil and assigned it to the species Lycosa florissanti, from a well-preserved fossil specimen.

Spiders belong to the class Arachnida. Unlike insects, arachnids have eight legs instead of six, have two body sections instead of three, and do not have antennae or wings.

Taxonomy of wolf spider from the Florissant Fossil Quarry
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Araneae
Suborder: Labidognathidae
Family: Lycosidae

These spiders are incredibly successful – with a lineage stretching back millions of years. With over 100 genera and 2,300 species, they are capable predators spread throughout the entire globe and can inhabit almost every type of environment. From shrub lands to coastal forests, from gardens to alpine meadows, most of these spiders are wanderers and vagrants, with no fixed home, and can live just about anywhere (Wolf Spiders in Nebraska).

Florissant spider specimen
Fig. 1. Fossil spider (family: Lycosidae). The rock is split along the bedding plane of the ancient Lake Florissant shales. Found at the commercial fossil quarry, near to the Florissant Fossil Beds National Monument. Scale bar in centimetres. Photo by SW Veatch.

Wolf spiders hunt in many different ways, depending on the species, size, prey types and habitats. These spiders are known to ambush and even chase down insect prey. Some species jump from hiding to pounce on prey. These organisms are important controllers of harmful insects and, even though they can be dangerous to people, their presence is generally considered favourable. Most of the few species that stay in one place throughout their lives live in small burrows lined with webs. They simply sit inside and wait for prey to come close, and then spring from their burrows and attack. Some desert-dwelling, burrowing wolf spiders will even plug their burrows with leaves and pebbles to avoid flooding (Wolf Spiders).

Wolf spiders range in body size from 10.2mm to 30.5mm long and can be even larger in diameter with their legs outstretched. In some species, the venom is mild, but, in others, it is potent and is known to cause necrotic wounds, which create an area of dead flesh around the puncture site (Isbister and Framenau, 2004). Most of the species that have necrotic bites are native to South America and Australia (Ribeiro et al., 1990).

The identification of fossil spiders at Florissant remains difficult, because they tend to be poorly preserved, owing to their soft bodies as compared to the harder bodies of insects. This wolf spider – found on a sunny summer day in 2012 – is no different from the other fossil spiders found in the area, which have only left unclear impressions in the shale, making identification to species level all but impossible.

References

Isbister, G. K., and Framenau, V. W. (2004). Australian wolf spider bites (lycosidae): Clinical effects and influence of species on bite circumstances. Clinical Toxicology, 42 (2), 153-161.

Meyer, H. (2003). The Fossils of Florissant. Washington: Smithsonian Books.

Petrunkevitch, A. (1922). Tertiary spiders and opilionids of North America. Transactions of the Connecticut Academy of Arts and Sciences, 25, 211-279.

Rasnitsyn, A. (2012, June 1). Entomologist, Russian Academy of Sciences, Moscow. [Personal Communication].

Ribeiro, L. A., Jorge, M. T., Piesco, R. V., & Nishioka, S. A. (1990). Wolf spider bites in São Paulo, Brazil: A clinical and epidemiological study of 515 cases. Toxicon, 28(6), 715-717.

Wolf spiders in Nebraska. (n.d.). Retrieved from http://lancaster.unl.edu/pest/resources/wolfspider.shtml.

Wolf spiders. (n.d.) Australasian Arachnology Society, Retrieved from http://www.australasian-arachnology.org/arachnology/araneae/lycosidae.