Spiders in the genus Phrurotimpus are currently found in the equally difficult-to-pronounce family of Phrurolithidae (they've also been assigned to Clubionidae, Liocranidae and Corinnidae in their taxonomic history). According tot the World Spider Catalog, there are 26 described species with 23 of them known from North America (the other 3 are known from China). It is possible that there are additional species waiting to be discovered or at least described. Dondale & Redner indicated they thought that the genus was in need of revision (1982) and Platnick's revision of the palustris species group is the only work that has been done since (2019).

On iNaturalist this genus of spiders goes by the common name of Antmimic Corinnine Spiders which keeps with the theme of making their name difficult to say. Dondale and Redner (1982) described them as "somewhat antlike" but I have never considered them as such and there are several more convincing ant mimics in Minnesota's spider fauna. I prefer the common name of Guardstone Spiders which is often applied to the family. That name is consistent with my experience that they are often under rocks on the ground (though not exclusively).

The overall impression of these spiders is a small, slender, fast moving ground spider (Dondale and Redner, 1982 indicates a maximum of 3.5mm). The first pair of legs is longer than the others and in males is often marked with dark patellas and tibiae bordered by a pale band on the lower tibia. Males can have a iridescent sheen to them; females (and sometimes males) have a pattern of chevrons on their abdomen.

These spiders are found in the leaf litter as well as under logs and stones in a variety of habitats. Due to their quick movement and small size, they are challenging to capture alive. They overwinter in their penultimate instar (one molt away from maturity) and mature in late spring or early summer; females attach their shiny, flat, red egg sacs to the underside of stones (Dondale & Redner, 1982). An example of their egg sac can be seen here: https://bugguide.net/node/view/309186/bgimage.

The genus Phrurotimpus in Minnesota is represented by four species.

P. alarius is only known from two counties in Minnesota: Nicollet and Mille Lacs. Kaston (1948) indicates this species has black/gray spots [bands] on legs III and IV. A female can be seen here: https://www.inaturalist.org/observations/5288693.

P. borealis is known from six counties across the state. It is known from Fillmore County in the southeast west to Blue Earth County and north to Lake of the Woods and St. Louis Counties. Female: https://www.inaturalist.org/observations/5288727 and male in alcohol: https://www.inaturalist.org/observations/82077141.

P. certus was first found in the state in 2022 and is only known from Pipestone County at this time. These individuals were very brightly colored and I knew it would be a new species of Phrurotimpus for the state when I first saw them. Female: https://www.inaturalist.org/observations/123708947 and male:https://www.inaturalist.org/observations/123262525.

P. palustris is known from three counties in the southeastern part of the state: Rice, Wabasha and Winona. There are no pictures of this species on either iNaturalist or BugGuide yet and Minnesota records were gleaned from Platnick, 2019. Platnick indicates that this species has dark bands on Legs III and IV and therefore is most likely to be confused with P. alarius.

Happy spidering!

Sources:
Dondale, C. D. & James H. Redner. 1982. The sac spider of Canada and Alaska (Araneae: Clubionidae & Anyphaenidae). Agriculture Canada, 1724:1-194.

Kaston, B. J. 1948. Spiders of Connecticut. Bulletin of the Connecticut State Geological and Natural History Survey 70: 1-874.

Platnick, Norman I. 2019. The Guardstone Spiders of the Phrurotimpus palustris Group (Araneae, Phrurolithidae). American Museum Novitates 3944:1-29.

World Spider Catalog-Phrurotimpus: https://wsc.nmbe.ch/genus/576