Opposable spines facilitate fine and gross object manipulation in fire ants

Abstract

Ants inhabit diverse terrestrial biomes from the Sahara Desert to the Arctic tundra. One factor contributing to the ants' successful colonization of diverse geographical regions is their ability to manipulate objects when excavating nests, capturing, transporting and rendering prey or grooming, feeding and transporting helpless brood. This paper is the first to report the form and function of opposable spines on the foretarsi of queens and workers used during fine motor and gross motor object manipulation in the fire ant, Solenopsis invicta. In conjunction with their mandibles, queens and workers used their foretarsi to grasp and rotate eggs, push or pull thread-like objects out of their way or push excavated soil pellets behind them for disposal by other workers. Opposable spines were found on the foretarsi of workers from seven of eight other ant species suggesting that they might be a common feature in the Formicidae.

Fire ants self-assemble into waterproof rafts to survive floods

“…Conversely, the gripping force is twice as strong as the ant adhesion to smooth surfaces such as glass (370 AE 90 dyn, N ¼ 10) or plastic (1-150 times body weight) (20,21). On such surfaces, ants extrude fluid drops with their feet, adhering using the associated capillary and viscous forces (18,22,23).…”

Functional diversity of attachment and grooming leg structures is retained in all but the smallest insects

“…Beginning with the last category, it is well known that legs and leg armament can be used for prey capture in insects through clasping between two or more segments (Oufiero, 2019; Olmi et al ., 2020), the increase in friction or adhesion via arrays of various hair‐like structures (Zhang & Weirauch, 2013), impalement (Rivera & Callohuari, 2020) or even 'stomping' (Betz & Mumm, 2001) among other mechanisms. Notably, tarsal setation, in opposition with the tarsal annuli, has been suggested to be used for grasping in ants (Cassil et al ., 2006). Communication is exceptionally well studied in the Formicidae, wherein over 20 distinct exocrine glands are known from the legs (Billen, 2009, 2019), many of which are derived for trail‐laying (see Hölldobler & Wilson, 1990, for example), and more than a few have patently uncertain function, such as the 'toothpaste gland' of Melissotarsus (Hölldobler et al ., 2014).…”

Ambidextrous Mandibles in the Fire Ant Solenopsis invicta

“…Exceptions to the triangular mandible morphology are ants with short, narrow mandibles, long-toothed mandibles (Eisner et al 1996), sickle-like mandibles (Gronenberg 1995), single-toothed mandibles for puncturing the soft cuticle of prey, or multipletoothed mandibles for cutting or grinding the harder cuticle of plants and prey (Wilson 1980). A serendipitous observation made during a study on the form and function of the red imported Þre ant, Solenopsis invicta Buren, appendages (Cassill et al 2007) found that their mandibles overlapped in two orientationsÑright overlap or left overlap (Fig. 1).…”

“…The family of ants (Formicidae) recently joined the families of preying mantids (Mantodea) and mantid lacewings (Neuroptera: Mantispidae) as insects that manipulate objects with grasping forelegs (Cassill et al 2007). In combination with their forelegs, ants use their opposing mandibles for a diverse set of functions.…”

“…In combination with their forelegs, ants use their opposing mandibles for a diverse set of functions. For example, ants hold brood gently with their mandibles during grooming (Cassill et al 2007) or while transporting brood from chamber to chamber inside the nest. Ants also use their mandibles for hard manual labor such as nest excavation (Cassill et al 2002) and warfare, defense, hunting, foraging, or butchering prey (Hö lldobler and Wilson 1990, Gronenberg 1995, Gronenberg et al 1997, Cassill et al 2005.…”