A special characteristic of P. festivus, which it shares with other Phrurolithidae species, is the imitation of ants in the form of Batesian mimicry.

[2] Legend for indicated directional positions: In this species, the opisthosoma (abdomen) appears angled and about the same width anteriorly (front) as posteriorly (back).

In addition, as is common in Phrurolithus, the male has a scutum (sclerotized, or hardened plate) on the opisthosoma, which the female lacks.

The opisthosoma of the female has dorsally a dark brown ground coloration as well as iridescent setae (chitinized hairs).

The dorsal side of the opisthosoma shows a black coloration in the male, while there are two spot-like formations of white setae anterolaterally.

A single pedipalpus can sometimes be distinguished from those of other male Phrurolithus by the retrolateral (laterally recessed) apophysis (chitinized process) on its tibia (splint), which is very large in comparison here and has a shovel-shaped appearance.

The basal (located at the base) part of a bulb (male sex organ) of the species is prominent.

[1] The epigyne (female sex organ) of P. festivus is sometimes characterized within the genus by its posteriorly sclerotized (hardened) plate.

[5] In Phrurolithus minimus the pedipalps of the male are black striped and a single tibial apophysis attached to it is strongly curved.

[6] For Phrurolithus nigrinus, the curved tibial apophysis with a long, separated apex on a single pedipalpus in the male is most typical, while the epigyne of the species is characterized by a large median pit.

[9] The original range of P. festivus extended over Europe, North Africa, Turkey, Caucasia, Russia (European to Far Eastern part), Kazakhstan, Iran, China, Korea, Japan.

Also in Europe itself the species is represented area-wide and is missing in continental Europe only in Croatia, Bosnia and Herzegovina and Kosovo as well as additionally on the Russian double island Novaya Zemlya, in Franz-Josef-Land, Iceland and on the archipelago Spitsbergen, Sardinia, the Balearic Islands, Crete and Cyprus.

On Great Britain it is common especially in the southern part of the island, while its occurrence there is highly scattered in the west.

[11] Other proven habitats of the species include dry grasslands, dune heaths, ground litter under juniper (Juniperus), and the underside of stones on limestone surfaces.

The circadian (sleep-wake rhythm related) activity of the species ranges from about 7:00 a.m. to 9:00 p.m. during the day and thus largely corresponds to that of the trail ants.

Phrurolithus festivus is euryphagous (not dependent on specific food) and consequently an opportunistic hunter that preys on other arthropods.

In captivity, the killing of springtails (Collembola), fruit flies (Drosophilidae) and homopterans (Homoptera), and thus of prey smaller than 70% of the body length of the spider, has been demonstrated.

Some smaller invertebrates, including springtails and mites, do not receive attention from the ants where P. festivus resides and can therefore be used by it as food in large quantities.

[10] The life cycle of the spider, in addition to the prey spectrum, was analyzed in parts in 2011 by Stano Pekar and Martin Jarab.

This process occurs in P. festivus during daylight hours and on open surfaces such as tree bark or the substrate, so unlike some other myrmecomorph spiders, mating here does not involve protective measures during reproduction.

In some other spiders with this trait, such as the unrelated ant jumpers (Myrmarachne), mating takes place in a web.

Although this is also the case with other myrmecomorph spiders and can be attributed to the narrower opisthosoma in favor of the ant-like shape, the low number of laid eggs in P. festivus is probably due to the generally rather short body length of the species.

According to Pekar's and Jarab's observations, a mated female of P. festivus produces on average two egg cocoons in succession at certain time intervals.

However, since cocoon numbers are significantly lower in less myrmecomorphic spiders, such as P. festivus, it has also been shown that iteroparity (ability to reproduce multiple times) is not affected by mimicry.

In addition, its myrmecomorphic appearance also serves as protection against other predators hunting by means of optical perception besides birds, such as reptiles like skinks.

However, the myrmecomorphic appearance of P. festivus, apart from predators that use their sense of sight for hunting, proves effective on those that hunt by means of chemical stimuli, including digger wasps (Spheciformes).It is assumed that these parasitoid wasps can identify their preferred prey, including spiders, on the basis of the chemical structure of its integument (outer body shell).

It is less myrmecomorphic than, for example, spiders from the genus Myrmarachne, in which the resemblance to ants is even more pronounced due to the shape of the body and legs; these two habitual characteristics are missing in P. festivus.

It has been experimentally demonstrated that birds have difficulty distinguishing myrmecomorph spiders from ants using their sense of sight.

[21] At its first description in 1835 by Carl Ludwig Koch, it was subdivided by the author of the genus Macaria under the name M. festiva.

However, Koch himself subordinated it already four years after his first description to the genus Phrurolithus, which was also first described by him at that time, under the still common name P. festivus.