Observations on the diet of Lygodactylus, a diurnal, semi-myrmecophagous gecko, in East Africa

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Here are my observations on the diet of Lygodactylus (https://en.wikipedia.org/wiki/Lygodactylus). These were made in the Pangani area of the East African coast (https://en.wikipedia.org/wiki/Pangani).
 
The point of special interest is that Lygodactylus is among the few geckos on Earth that is relatively specialised for myrmecophagy. True myrmecophages take ants and termites as more than 75% of the volume of food in their overall diet. It is unclear from the literature whether Lygodactylus meets this criterion.
 
Bill Branch (1988), in his field guide to the reptiles of southern Africa (https://books.google.com.au/books/about/Field_Guide_to_Snakes_and_Other_Reptiles.html?id=BIErAQAAMAAJ&redir_esc=y), calls Lygodactylus 'dwarf geckos'.

Branch states that they “eat ants and termites, and can be seen stationed next to their trails, picking off victims.” The best-known southern African species, Lygodactylus capensis, “prefer to forage in low scrub and on dead trees, and feed almost exclusively on termites.” Lygodactylus chobiensis, which forages high in trees, “feed on termites” (Branch 1988).
 
I tested these generalisations by making/supervising original observations near my lodgings in Tanzania, in May 1993. The subject was an unidentified, diurnal species in this genus, probably Lygodactylus picturatus (https://www.inaturalist.org/taxa/34238-Lygodactylus-picturatus).
 
LOCATION

Mkwaja Ranch, which is now next to the northern part of Saadani National Park, Tanzania (https://en.wikipedia.org/wiki/Saadani_National_Park). This is on the coastal mainland, opposite Zanzibar.

See https://www.sciencedaily.com/releases/2010/05/100504143527.them and https://www.yumpu.com/en/document/view/50442973/ecosystem-studies-on-the-former-mkwaja-ranch-and-the-new-s and https://mapcarta.com/12652574 and https://www.mindat.org/feature-153448.html#:~:text=Type%3A,Pangani%20District%2C%20Tanga%20Region%2C%20Tanzania.

METHODS

Members (all adult) of 10 groups of Lygodactylus sp. were observed for 20 consecutive days, during the main rainy season of 1993, in the semi-wild garden of a ranch homestead. No observations were made at night. A total of ca 50 individuals was observed, collectively for a total of more than 100 hours. At any one moment, usually 2-4 individuals were under observation. A different group (on a different tree or building) was visited and observed each day, usually by spending most of the day (except for mealtimes) with that group. All foraging bouts were recorded.

Also see below for inadvertent experiment involving carob and sausage tree fruits.
 
RESULTS

Lygodactylus sp. proved to be an ant- and termite-eater, but not a specialised myrmecophage.

A total of about 150 instances of eating (pecking) were recorded.
 
The geckos foraged mainly on trees and walls, but also ventured on to the ground. They were not seen taking ants or termites on the ground. The largest items swallowed were orthopterans (probably crickets), not much longer than the gecko’s head.
 
Ant workers (one small species 2 mm long, and another of modest size, 4 mm long) were usually present with the geckos, but were generally not eaten. The ants that were eaten seemed to be alates, or eggs and pupae carried by worker ants.

Small termites were present on most trees inhabited by the geckos, within covered runways running up and down the boles. The termites within were available only where the tunnel covering had been breached. Geckos were not observed to breach termite runways.

The lizards foraged on open surfaces. They neither foraged, nor sought refuge from potential predators, under cover such as crevices or the runways of termites. I do not know if they retired to cover at night. On the one occasion in which an individual gecko was found foraging from a breached runway of termites, the same individual took > 25 individuals of the termites, standing by the column of workers as Bill Branch implies.

It is unlikely that ants and termites contributed > 75% of food volume, as follows.

Termites and ants contributed an estimated 50% (half) of all items pecked and eaten (50% of pecks) during these observations. I do not know whether this would hold good also for food volume. The other 50% comprised various invertebrates (of various sizes, from tiny to about the head size of the gecko), and a noteworthy if limited incidence of plant matter, in the form of exudates.

The plant exudates were from

• growing shoots of e.g. Citrus sp.,
• carbohydrate-rich surfaces of broken pods of Ceratonia siliqua (carob, actually legume pods of a special type, brought by Antoni from Perth to Tanzania, https://www.inaturalist.org/taxa/82742-Ceratonia-siliqua), and
• presumably carbohydrate-rich surface of cut fruits of sausage tree Kigelia africana (https://www.inaturalist.org/taxa/81491-Kigelia-africana), indigenous to the study area.

I had placed the broken/cut pods and sausage fruits on a verandah. These were visited with apparent enthusiasm by one individual among the resident geckos.

Please note that the fruit-fragments of neither carob nor sausage tree were initially placed with any intention of attracting geckos; the 'baiting' was inadvertent. Since these observations were opportunistic, no experiment was attempted to test whether the geckos would visit other, sweeter/more succulent fruit slices. However, my impression was that they would have done so.
 
In summary:
Termites may be the main diet on trees, where termites are present and accessible. However, Lygodactylus sp. accepted a wide range of other foods including some carbohydrate-rich plant matter. It is very selective when eating ants. Hence, on the basis of limited sampling, this species (probably L. picturatus) cannot be considered to be a lizard specialised for eating ants and termites. These results tend to undermine the generalisation of myrmecophagy at the genus level in Lygodactylus. 'Semi-myrmecophagous' seems to be a more accurate description.
 
DATA

A. Frequently-taken types of food: 

• small termites on tree stems;
• gnat-like wingless insect, found on walls; much smaller than the termites; only half the size of the little ants (length 2 mm) that the same geckos did not eat, despite their frequent availability; and
• ‘sap’ oozing from shoots, particularly of Citrus, but also Delonix and Plumeria, in garden.

B. Infrequently-taken types of food: 

• winged ants (alates) emerging as individuals from cracks in tree trunk;
• ant pupae;
• black ant workers (4 mm long);
• unidentified wingless insect;
• tick-like insect;
• unidentified winged insect;
• beetle-like insect; and
• small orthopteran insect taken on the ground.

C. Rarely-taken types of food: 

• white exudate of scale insects;
• fruit fragments of carob and sausage tree, of which the already cut surfaces were licked by the geckos;
• fruit flies;
• inchworm (loop caterpillar);
• spider; and
• small moth.

Posted on 15 de julho de 2022, 09:30 PM by milewski