No need for a spoiler alert here. Toad imagery and symbolism is a big part of "Toads." Larkin makes good use of our amphibian friend's long symbolic tradition and all of the slimy, warty, negative associations that go along with it. Throughout history, toads pop up as everything from poisonous witches' companions to all-around harbingers of death. Not cool.
Note: If you're one of those folks that have a desk or a dresser covered with adorable toad tchotchkes (you know who you are), you can stop yelling at your computer screen. You're perfectly entitled to think toads are wonderful, cuddly creatures. We get it. Some people like those little warty guys. To each their own. We just want you to understand that your toads aren't the kind Larkin had in mind. Now, let's take a look at how Larkin uses his toads in "Toads."
Title: Larkin doesn't waste any time. He puts our slimy friend right there in the title. Not only is "toad" in the title, it is the only word in the title. Larkin wants to make sure that the toad image squats in our minds for a second or two, without any distraction or other context, before we start reading the poem. As a result, we bring all those slimy associations with us as we begin reading the poem's first few lines.
Lines 1-4: In the poem's first stanza, we discover that Larkin is using the toad metaphorically to represent work. The slimy associations that we carried with us from the title get connected to the mention of work in stanza 1. As a result, we don't think about rewarding careers and the feelings of accomplishment that come from doing a worthwhile job that we like. Nope. We picture the ugly, brutish, soul-crushing kind of work that prevents one from living a full, content life.
Lines 5-6: If there was any doubt that Larkin wanted us to be thinking about the traditionally negative aspects of toads and associating those aspects with work, lines 5 and 6 make his intentions crystal clear. The toad (work) "soils" the speaker's life "with its sickening poison." Yuck.
Lines 25-28: Our slimy little friend hops into the picture again in stanza 7, but this time something's a little different. The speaker confesses that, in addition to having the toad work squatting on his life, poisoning everything from the outside, there is something "toad-like" squatting in him as well, poisoning things from the inside. Our poor speaker just can't seem to get away from the slime. And this internal toad is no picnic. Its substantial—"heavy as hard luck, / And cold as snow." Walking around everyday feeling like you have something big, slimy, and cold hunkering inside you is no way to go through life.