Hummingbird feeders, rather than dispensing seed, supply liquid nourishment to hummingbirds in the form of a sugar solution. This mixture is often colored red to attract birds. Likewise, some Hummingbird feeders have red accents or red glass to help attract hummingbirds. Yeasts tend to grow in hummingbird feeders and spoil the solution, so they must be refreshed frequently and kept very clean to avoid harm to the birds. See the article on hummingbirds for more details. Ants and other insects are also attracted to hummingbird nectar. Smearing petroleum jelly on the feeder's may prevent the ants from crawling to the feeder, but the birds cannot clean the petroleum jelly from their feathers, so alternative methods should be found.