The Myxomycota, commonly known as slime moulds do not belong to the fungi kingdom, but in many aspects they are fungi-like and are studied by mycologists. Slime moulds belong to the kingdom Protoctista.
Slime moulds live in damp terrestrial habitats such as below garden mulch or forest-floor debris, and inside decaying logs.
#3 Fruiting bodies of slime mould in my garden
#4 When damaged, the crust breaks to reveal spores
Image #2 is a pale pink version of the same fruiting bodies as in image #1, photographed on the same day on mulch.
Image #4 is the same species with the crusty exterior cracked to expose spores.
Images #5, #6 and #7 are the same slime mould photographed in May 2007 on leaf litter in alpine woodland. Pic 5 shows the active mobile stage, pic 6 shows the separating stage, and pic 7 shows the sporangium formed. The sporangia will dry out and crack to expose spores to be dispersed by the wind. Fifteen hours elapsed between picture 6 and 7.
#7 Sporangium (spore bearing capsules) of the slime mould of previous two images
There is no cause for alarm if you find these creeping slimy growths in your lawn or garden. They will not harm your pets if injested, and there is no evidence that they cause harm to plants.