Who are Those Ants in Our Homes and Gardens?

August 11, 2012

Lots of people in the L.A. area have been complaining about the heat. Over the last week, cities in our region have been experiencing temperatures well into the 90s. On Monday, Woodland Hills reached 108 degrees!Whenever the temperature rises like this, I start to notice ants indoors. Only this morning during our Nature Lab meeting, I found a trail of ants leading to the sink, and another leading to the snack shelf.The ants I found are Argentine Ants, Linepithema humile. They are an introduced species from South America (Argentina and Brazil) and are now considered the most common ant in our area. According to the Insects of the Los Angeles Basin book, these ants were "introduced to New Orleans before 1891 in coffee shipments from Brazil, and it has since spread rapidly over much of the United States."This is what the same book has to say about their pest status:"The species is one of the most persistent and troublesome of all our house-infesting ants. Argentine Ant workers seek out and feed on almost every type of food, although they are especially fond of sweets. Making themselves most objectionable, the ants invade the house through minute crevices and cracksfiling along baseboards, across sinks, and over walls and tables in endless trails."How do you feel about ants in your home? While writing this blog, I've found it interesting to ponder this question. As you may have noticed I am a nature lover, however I am definitely not a fan of ants in my house and will go to great lengths to remove them. Many times this feels like a losing battle, especially because I'm not one for spraying pesticides all over the place I live.

Argentine Ant about to take drink of water in our Nature Lab trailer(It is one eighth of an inch long)The Argies, as we "fondly" refer to them, have also been found throughout the North Campus. This isn't surprising as it is well documented that this ant species has displaced many of our native ants. According to Alex Wild, author of the Myrmecos ant blog, Argentine Ants, "can drive native arthropods to extinction, instigating changes that ripple through ecosystems. In California, horned lizard populations plummet. In South Africa, plant reproduction is disrupted. Worldwide, the Argentine Ant is a persistent house and crop pest. This is not a good ant." Here are some pictures of their activities on the North Campus:

Argentine Ants killed all the paper wasps in this nest

Argentine Ants tending citrus scales in our orange treesWhen I found the ants had killed all the paper wasps in the nest pictured above, I have to admit I was disappointed. I know many would be cheering for the ants, as paper wasps are viewed as a pest themselves. However, I had already become invested in the livelihood of that particular wasp nest and would check up on it every time I was out in the gardens. I find it infinitely interesting to ponder our notion of pest. What is acceptable in some circumstances is unacceptable in others. However, I still haven't come across anyone who is a fan of Argentine Ants!Need tips of managing ants in your home? Check out the UC Davis Integrated Pest Management website.


(Posted by: Lila Higgins)


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March 9, 2012

I was recently out and about in the garden and found some fascinating insects, Keelbacked Treehoppers, Antianthe expansa. They were on some of our celery plants and are, according to Vanessa Vobis Master Gardener and Museum Gallery Interpreter, "a very annoying pest on our tomatoes."

Adult Keelbacked Treehopper on celery(Approximately ¼ inch or 7 mm long)When I found the Keelbacked Treehoppers, all but one were in the nymphal (immature) stage. As nymphs, these insects do not have wings (this is true for all insectsjust look at caterpillars, grubs, and maggots), and are bound to the area in which they were deposited as eggs by their mother. The nymphs are often attended by ants, which feed on their sugary excreta and provide a level of defense against the treehopper's predators. Though it should be noted that this is not always the case, there were no ants in attendance around the treehoppers I found, so this isn't a reliable mode of identification.   When I found the treehoppers in our Edible Garden, they were feeding on one of the celery plants. They feed on the juices (phloem sap to be exact) inside the plant by inserting their tiny straw-like mouthparts and sucking up the liquid. Although many sources say that these insects cause little, if any, damage to the plants they are on, this is not always the case! When populations of these insects are high enough they can cause serious stunting and sometimes lead to the loss of plants. Many gardeners in our area complain of these pests on their tomatoes. It is not clear if the decline in plant health is due to excessive feeding by these insects or by secondary infections spread to the plant during feeding. 

Immature Keelbacked Treehopper photo courtesy of Vanessa VobisFrom a naturalist's perspective these insects are some of the more weird and wonderful. Adult treehoppers (family Membracidae) can be recognized by the prominent enlargement of the pronotum (segment directly behind the head). This enlargement gives many treehoppers a humpbacked or thorny look, hence the other common name for these insects: thorn bugs. However, some tropical species go beyond the thorny devil look and opt instead for something a bit more insectuous! Case in point, the Cyphonia treehopper has a pronotum that mimics an aggressive ant species, which not only looks awesome, but is a great defensive mechanism against predators.      

Cyphonia treehopper with ant-like pronotumimage from Nicolas Gompel/Nature 


(Posted by: Lila Higgins)


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