The ability of this species to defend itself with a particularly
odiferous secretion was reported as early as 1835, when Gray in
describing the genus quoted an account by Thomas Say "...that when
taken they discharged a milky fluid from two pores of the thorax,
diffusing a strong odor..." Albert (1947) also described it as a
"...rather thick, tenacious white material..." Blatchley (1920)
described it as having "...a peculiar, though somewhat pleasing
odor, which has been likened to that of the common everlasting,
Gnaphalium obtusifolium L." MacAtee (191
reported a second hand report "...that Anisomorpha
buprestoides discharges a vapor from the end of the abdomen and
that the discharge is preceded by a peculiar crepidation..." He
noted, correctly, that this report differs from almost all
others.
Eisner (1965) reported, "The secretion is produced and stored in
two elongate, sac-like glands situated in the thorax and opening
just behind the head." Happ et al. (1966) presented detailed
information on the structure of the glands. The glands open in
notches at the anterolateral angles of the pronotum (Littig 1942).
The glands are functional from birth and Eisner (1965) reported
newly-hatched nymphs successfully repelling attacks by single ants.
Meinwald et al. (1962) identified the active ingredient as a
terpene dialdehyde related to catnip and named it
anisomorphal.
pronotal gland
Eisner (1965) reported that the stick insects generally discharged
the secretion as a result of certain perceived threats. They can
aim up to 30 to 40 cm with accuracy: "Anisomorpha discharges
instantly in response to mild traumatic stimulation as, for
example, when individual legs are pinched with forceps, or when the
body is tapped or persistently prodded . . . Marksmanship is
precise: the spray invariably drenches the particular instrument
used for stimulation." Although most discharges required actual
physical contact, Eisner (1965) found that the stick insects often
would discharge at birds before being contacted by the bird. In
trials, Eisner (1965) found the secretion to be an effective
defense against ants, beetles, mice and birds; mouse- opossums
(Marmosa sp.), however, managed to withstand the spray and consume
the stick insect once its reservoir was depleted after up to five
discharges from the larger females. One to two weeks are required
to replenish the depleted reservoirs (Eisner 1965). Carlberg (1985)
found that rats (Rattus norvegicus (Berkenhout)) initially were
repelled, but some individuals managed to overcome the defense in
subsequent attacks.
