If you are roused in the middle of the night by the loud thump of a falling coconut, you may reconsider your decision to park your bike under a palm tree. This is a natural reaction: falling coconuts can crack a human skull; no doubt they can split open a plastic gas tank or sever a clutch lever or other vital bike part. At dawn, when you wake you may uncover your bike in preparation to roll it into a coconut-free zone and in doing so discover that a colony of ants has taken up residence in your helmet. You’ll no doubt begin swiping away at the superorganism without any thought as if they are the biting kind of ants. You then will realize that the dozens of ants you’ve already swept away are now crawling on your arms and ankles, and you haven’t felt a sting, so you can be confident they aren’t aggressive. Good. At this point you will want to learn the word "myrmecophobia"; you'll be needing it from now on. Now, while you contemplate how to end this nightmarish vision of a hundred crawly things circling in and out of every hole on an effigy of your head, explore the following options:
1) Buy a pack of cigarettes. Smoke a half dozen over the course of the day, strategically exhaling each mouthful of CO2 into the helmet’s ventilation holes, smoking the little buggers out. This method has the upside that, with over a dozen of unlit cigarettes remaining in your possession, you can share with locals and build street cred. The downside is that smoking a half dozen cigarettes on a hot and humid day is nauseating.
2) Submerge the helmet in a pool of water. The difficulty here is finding a pool of relatively benign water. You may be 50m from all the water the Pacific has to offer, but the residual scent of a Delaware marina in immediate proximity to your nostrils will deter this instinct. The spigots at the campground could provide a cleaner, albeit imperfect option, but you are still left with the task of finding a bucket large enough that you can fully submerge the helmet.
3)Purchase a good quantity of rubbing alcohol and pour it into the various ventilation holes of the helmet. Ignore the pharmacist's expression when you ask to buy all the bottles they have for sale. This method has the advantage of disinfecting the helmet, not only the ant carcasses but also the sweaty funk accumulated from months of riding in hot weather. However, the pouring technique allows the little buggers to run around and avoid whatever path your murder juice is flowing down. They didn't survive the Cretaceous–Paleogene extinction event 65 million years ago for nothing.
If all of these options are available to you, the following combination will likely work best. Use the spigot to pour water into the helmet holes and swirl it around. About 5-6 ants will come out of their hiding spots. Flick them off and continue swirling. Repeat throughout the helmet until there are no signs of life. Let dry. Once dry, pour a bottle of rubbing alcohol through the various holes. Swirl. Watch 3-4 stumble out intoxicated. Flick them off. Continue swirling. Let dry. Repeat the above again with water, then alcohol, until no evidence of life exists.
Congratulations, you have just completed an act of mass insecticide. Now you are only left to deal with the crippling fear of a host of those buggers coming out of the deep corners of your helmet while you ride down a narrow jungle highway at 70 mph. Safe travels!