Ants and Insectivorous Plants

Frank M. Jones

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Ant visits to the flowers

The flowers of the Sarracenias are quite commonly visited by numbers of ants, though the flower structure does not seem to indicate any adaptation for pollination through the agency of these small insects, which also continue their visits to the unripe ovaries, which too secreted nectar. Probably a number of ant species are included in this habit. Specimens of those visiting the flowers and nectarines of S. flava were identified for me by Dr. W. M. Wheeler as Tapinoma pruinosa Roger.

Ants and other insect visitors

Without relationship to the trap structures of the plants, other insect associates are sometimes responsible for the visits of ants. The hollow frass tubes of the Noctuid, Papaipema appassionata Harv. are occupied as nesting sites by a small ant which Dr. Wheeler identified for me as Prenolepis parvula Mayr.; and another ant which occupies cavities in the root stocks of these plants (probably cause by the larvae of this same insect) was indicated as Solenopsis sp.

My first paper described and illustrated the use of the pitchers of Sarracenia as nesting sites by the solitary wasp Isodontia harrisi Fernald; and ...later observations [show that] that habit was determined to be widespread (North Carolina to Mississippi inclusive), and that all suitable pitchers (those of S. flava, S. minor, S. sledgei, S. drummondii, S. rubra, S. jonesii) were thus utilized. Almost as widespread as the use of these pitchers by the wasp, were observations that the nests of the wasps, stored with Oecanthus or with small green grasshoppers, are systematically robbed of this stored food and with the resultant destruction of the wasp progeny, by ants which chew an entrance hole through the pitcher wall opposite the stored cell, and consume its contents. Preserved specimens (in coll) from one such occurrence were identified by Dr. Wheeler as Crematogaster lineolata var.; but where tall the observed instances of such robbery (Southern Pines, NC; Summerville, SC; De Funiak Springs, FL; Theodore, AL; Biloxi, MS) were the work of that same species, is not determinable from the evidence at hand.

Captures of ants by pitcher plants

The pitchers of the Sarracenias, when exuding their fragrant nectar bait, attract ants in large numbers. Sometimes a ring of ants, heads downward and closely side by side, may be observed within the mouths of these pitchers, evidently feeding in an area of abundant secretion; singly, ants may be seen to struggle upward on that treacherous footing, but the number of ants among the captures below indicated that they are frequently victims of the plant trap. This seems especially true when a populous ant colony exits in close proximity to the pitchers; and some species of the Sarracenias may seem almost to specialize in the capture of ants, rather than of larger and winged insects. The pitchers of Sarracenia minor are sometimes stuffed with ants for several inches of their height, and Dr. Wheeler's letter cited above says "The mass of ants in the pitcher plant Sarracenia major " (minor, sent for his inspection) "are almost exclusively soldiers and workers of Phediole morrisi Forel." The small diameter pitchers of S. rubra, too, are often most successful ant traps; and even purpurea, under favorable conditions, sometimes makes abundant captures of these insects. No attempt was made to identify the undoubtedly large number of ant species included among the captures of the Sarracenias.

Ants nesting in Sarracenia pitchers

The pitchers of most, if not all species, of Sarracenias are not infrequently occupied as nesting sites by several species of ants. Though those thus utilized are usually mature pitchers of a preceding season, their upper portions shriveled and dry, hence not fully effective as insect traps, occasionally such a colony may be found occupying a fresh green pitcher, destitute of the usual liquid secretion of the plant. Where the presence of the ants in some way produce that unnatural condition, or where non-secreting pitchers are chosen by the ants, was not determined.

The lower portion of the pitcher cavity, often with the dry remains of former insect captures or the litter of an old wasp nest is included; and such colonies were found with some frequency, whenever any considerable time was spent in examining the plants. The most perfect adaptation of this habit was exhibited by ants which ceiled off the lower portion of a pitcher tub with a dense plug of carton-like material, through which a small hole was provided for entrance and exit. A few collected specimens of these ants have been identified (1926) by Dr. Mann and his associated of the United States National Museum; the records of some of these, and of a few others not identified, are here included; and specimens of some are preserved in the collection:

• Dolichodoerus plagiatus; larvae and adults in a carton-ceiled pitcher of S. purpurea, Tom's River, NJ, VI, 9, 1915.
• Rapinoma sessile; larvae, pupae, workers, winged adults, in dead pitcher of S. purpurea, Tom's River, NJ, VII, 22, 1910.
• Prenolepis impars testacea, in S. purpurea, Southern Pines, NC.
• Leptothorax longispinosa, nesting in S. flava, Southern Pines, NC. Specimens of larvae and workers preserved.
• Unidentified species, nesting in S. purpurea at Southern Pines, NC, VII, 29, 1911; larvae, pupae, workers, winged adults preserved
• Unidentified species, nesting in S. flava, Summerville, SC, VII, 7 1916; pupae and workers preserved.
• Unidentified species found nesting in a carton-ceiled pitcher of S. rubra at Southern Pines, NC, April; a small pale species with the abdomen (workers) spotted laterally with red.
• Unidentified species: In March 28 at Theodore, AL, a large handful of the old pitchers of S. sledgei showed among them four pitchers housing colonies of ants; one species, small workers few in numbers but with a much larger queen; one much larger species, many workers, young, no conspicuous queen. In same locality, Apr. 24, in a pitcher containing the litter of an old wasp nest, an ant colony with workers, larvae, and pupae.

Many other records might be cited showing the widespread prevalence of this habit of utilizing the pitchers of Sarracenia as nesting sites. 

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