As far as I know, there are no herbivorous ants that directly eat plant leaves (not using the plant leaf as medium for fungi cultivation or other purpose). Does anyone know exceptions?
If not, are there explanations, physiological, ecological etc., as to why ants don't eat plant leaves directly?
To my knowledge, there are no exeptions. Ants most likely evolved from solitary hymenopteran predators and I think that they simply lack both the morphological and biochemical prerequisites to gain any immediate advantage from direct plant consumption.
Ok, an exeption I forgot may be the consumption of seeds in few ant taxa. The genera Messor and Pogonomyrmex rely not entirely, but very strongly on seeds as a food source. Additionally, there are some plants, so called myrmechores that develop, that attach elaiosomes to their seeds. The latter are consumed by ants and the seed thereby dispersed by ant foragers. However, in both cases there is no direct consumption of leaf material.
That sounds very interesting. In leaf-cutting ants, it is believed that workers partially feed on the liquids at the cutting edges while cutting the material. Do you know the species or genus? Have you seen them actually chewing the material or have they just cut it?
The acacia ant (Pseudomyrmex ferrugina) has formed a close symbiotic relationship with a particular species of acacia. The acacia produce 'beltian bodies' on the tips of their leaves which the ants consume. The plant also has large thorns which the ants hollow out and subsequently reside in. In return, the ants provide defence from herbivory and remove any competing vegetation. While beltian bodies technically aren't leaves (they are far richer in fats/sugars) they do seem to be modified leaves, so this is the closest example I can think of.
Hi Vera, thank you so much it's very interesting that you found Tapinoma ants directly damage young citrus leaves. Do you have publications about this discovery in English? or do you know other literatures talked about this ?
Hi Steffen, thanks for your information, concerning "...that they simply lack both the morphological and biochemical prerequisites to gain any immediate advantage from direct plant consumption..", as some plant-ants species need to and can dig holes as the entrances to their nest inside the hollow stem of their host plants, I thinks at least these ants' mouthparts should also be able to chew the plant leaves (I mean ants, at least some of them, have the ability but do not eat plant leaf, I am very intrested about why they don't? Vera's discovery about Citrus leaf damaging behavior of Tapinoma ants is a very important to understand this, but this needs more exploration about why Tapinoma ants damage the Citrus leaves, e.g. do Tapinoma ants eat the leaves or ...? and do they also do the similar damage to other plants).
Hi Jing-Xin, Veras observation is indeed fascinating. Concerning the use of mandibles to manipulate plant materials, I do see a problem. Unlike herbivore insects, ants have mandibles that are hardly useful ti chew plant material. They can of course cut it, but chewing for ingestion is a problem as the mandibles are sharply edged and overlapping like scissors. Ants ingest nutritients by means of a sucking mechanism that is has a limited tolerance to high viscosities. And there is little space to store and pre-digest solid components. I would generally say, the ingestion system of ants is widely adapted to handle and exchange liquids, the mandibles to cutting and carrying things. In leaf-cutting ants, that need the plant material chewed into more or less homogenous paste, the problem is solved by a strong size polymorphism: the fragments are cut smaller in consecutive steps by workers of decreasing body size.
Hi Steffen, thanks for your explanation about the features of ant's mandibles. May I ask a further question "do you know more ants that "cut" plant leaves in the field ?"
I don't know any examples. Some people say that wood ants cut away small plants from their trails to enhence movement, but I do not know whether that is fact and there are published observations or pure guess from the appearance of the trails. In some wood ants and few leafcutters, plant materials are used to build isolating thatches over subterranean nests, but the former rely on loose material, and the latter cut grass fragments anyway. So I think, leafcutters, and maybe the Tapinoma observed by Vera, are the only known exeptions.
Hi Jing-Xin,
maybe could you have a look at the following publication:
Explaining the Abundance of Ants in Lowland Tropical Rainforest Canopies. Science, 5/9/2003, Vol. 300 Issue 5621, p969
The authors cite different genera of ants such as Camponotus, Polyrhachis, cephalotes with a low 15N ratios and explain it by the consumption of extrafloral nectar and ... epiphylls (lichens, liverworts, and mosses growing on the leaves of other plants).
Once again, it's not the direct consumption of the leaf of an Angiosperm plant but it's getting quite close...
I hope this information will be helpful to you
The workers of leaf-cutting ants (genera Atta and Acromyrmex) ingests liquids coming from the cutting of leaves and this represents an important part of their nutrition, because, for example this fluid has simple carbohydrates that they can use as energy source. But the main food of ants Atta and Acromyrmex is your mutualistic fungus (Leucoagaricus gongylophorus), whose substrate for growth are fresh leaves of plants. The larvae of leaf-cutting ants are fed exclusively with this fungus. The fungus is able to degrade complex carbohydrates present in the leaves, such as starch, pectin and xylans (there are much controversy regarding the degradation of cellulose, but in my opinion, the mutualistic fungus is capable to degrade cellulose => http://www.jbr.gr/papers20112/16-Nagamoto%20et%20al.pdf ) into simple sugars as glucose, that is useful for the ants as energy source (adult workers, larvae and queen).
About other insects I know less well, but I believe that in ants and other hymenopterans in the suborder Apocrita ( http://en.wikipedia.org/wiki/Apocrita ), the herbivory is restricted to a few species and limited in quantity. However the suborder Symphyta is largely composed by "true" phytophagous (herbivorous) insects ( http://en.wikipedia.org/wiki/Symphyta ).
I found a kind of red ants attacked pods of longyard bean. They make hole and feed inside part of longyard bean's pod. Let us see whether the ant is belong to Selenopsis genus. Some collegues inform that ants are omnivore. Observation is still going on.
Hello Jing-Xin;
Here is an example that might be useful. Aphid-tending ants obtain a carbohydrate-rich food source. Wood ants in the genus Formica depend on this interaction for the carbohydrate portion of their diet and their habitat range is limited to plant communities that support large colonies of woodlice (Cinara spp.). These aphids feed on the needles of various conifers (Guariento, et al. 2018). These ants seem to have avoided the limitations of mandible structure that Steffen mentioned and at least nutritionally they gain an essential portion of their diet directly from leaves.
Guariento, E, D Rabl, S Ballini and K Fieldler 2018. Wood ants (Formicida, Insecta) at the alpine tree-line ecotone: negative and positive associations with other arthropods. Gredleriana 18:103-120.
Best regards, Jim Des Lauriers
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