In this paper we prove local existence of solutions to the nonlinear heat equation $$u_t = \Delta u +a |u|^\alpha u, \; t\in (0,T),\; x=(x_1,\ldots , x_N)\in {\mathbb {R}}^N,\; a = \pm 1,\; \alpha >0;$$ with initial value $$u(0)\in L^1_{\mathrm{{loc}}}({\mathbb {R}}^N{\setminus }\{0\}),$$ anti-symmetric with respect to $$x_1,\; x_2,\ldots , x_m$$ and $$|u(0)|\le C(-1)^m\partial _{1}\partial _{2}\cdots \partial _{m}(|x|^{-\gamma })$$ for $$x_1>0,\ldots , x_m>0,$$ where $$C>0$$ is a constant, $$m\in \{1, 2,\ldots , N\},$$ $$0<\gamma <N$$ and $$0<\alpha <2/(\gamma +m).$$ This gives a local existence result with highly singular initial values. As an application, for $$a=1,$$ we establish new blowup criteria for $$0<\alpha \le 2/(\gamma +m),$$ including the case $$m=0.$$ Moreover, if $$(N-4)\alpha <2,$$ we prove the existence of initial values $$u_0 = \lambda f,$$ for which the resulting solution blows up in finite time $$T_{\max }(\lambda f),$$ if $$\lambda >0$$ is sufficiently small. We also construct blowing up solutions with initial data $$\lambda _n f$$ such that $$\lambda _n^{[({1\over \alpha }-{\gamma +m\over 2})^{-1}]}T_{\max }(\lambda _n f)$$ has different finite limits along different sequences $$\lambda _n\rightarrow 0.$$ Our result extends the known “small lambda” blow up results for new values of $$\alpha$$ and a new class of initial data.